ACS CCN1 Core Domestic Gas Safety Assessment — Questions and Answers

Question 1: When a chimney serves an open-flued gas fire, what test must be carried out to confirm the chimney is safe to use?

A water flow test
An electrical continuity test
A pressure test at 200 mbar
A smoke test (flue integrity test) and spillage test (Correct answer)

Correct answer: A smoke test (flue integrity test) and spillage test

Before connecting an open-flued gas fire to a chimney, a smoke test (flue integrity test) must be carried out to confirm the chimney is structurally sound and does not leak combustion products. A spillage test must also be performed with the appliance operating to ensure the chimney provides adequate draught and products of combustion are safely evacuated.

Question 2: What does a yellow or orange flame on a natural gas burner indicate?

The correct operational colour for a gas burner
The appliance is in its warm-up phase and will correct automatically
High gas pressure causing excess fuel combustion
Incomplete combustion — insufficient air supply causing carbon particles to glow as the flame burns luminously (Correct answer)

Correct answer: Incomplete combustion — insufficient air supply causing carbon particles to glow as the flame burns luminously

A natural gas burner should produce a predominantly blue flame. A yellow or orange flame indicates incomplete combustion due to insufficient air, producing luminescent carbon particles (soot) and CO.

Question 3: What is the risk if a decommissioning purge is not carried out before dismantling a gas connection?

Only a minor smell of gas — not enough to cause explosion
Gas disperses instantly so no purge is needed before disconnecting
Residual gas in the pipe will escape when the connection is broken, creating an explosive atmosphere that can be ignited by any nearby ignition source (Correct answer)
Residual gas will only cause appliance malfunction, not explosion

Correct answer: Residual gas in the pipe will escape when the connection is broken, creating an explosive atmosphere that can be ignited by any nearby ignition source

Any residual gas in disconnected pipework will escape when the connection is broken. If sufficient gas accumulates and meets an ignition source (sparks, flames, static), it can ignite explosively. Decommissioning purge removes this risk.

Question 4: According to current gas industry guidance, how long should an engineer wait after purging before attempting to light an appliance?

30 seconds while operating the fan to clear the burner area
There is no waiting period — the appliance can be lit immediately after purging
10 minutes regardless of appliance type
The time specified in the appliance manufacturer's instructions — typically enough time for any residual air-gas mixture near ignition components to clear (Correct answer)

Correct answer: The time specified in the appliance manufacturer's instructions — typically enough time for any residual air-gas mixture near ignition components to clear

The manufacturer's instructions specify the required pre-ignition procedure, which includes any required purge period before attempting ignition. Following the manufacturer's instructions is mandatory under PUWER and the GSIUR 1998.

Question 5: What is the minimum internal diameter of a flue liner suitable for a standard domestic gas boiler?

125 mm (Correct answer)
150 mm
75 mm
100 mm

Correct answer: 125 mm

The minimum internal diameter for a flue liner serving a standard domestic gas boiler is 125 mm (approximately 5 inches). This applies to both rigid and flexible flue liners installed in masonry chimneys. The liner must be suitable for gas and must be installed in accordance with the appliance manufacturer's instructions and BS 5440-1.

Question 6: What percentage of CO2 would you typically expect in the flue gases of a correctly adjusted natural gas boiler?

4–6%
7–9% (Correct answer)
Less than 3%
12–14%

Correct answer: 7–9%

A correctly adjusted natural gas boiler running with the appropriate amount of excess air should produce approximately 7–9% CO2 in the flue gases, indicating efficient combustion.

Question 7: What is the correct immediate action if a gas smell is detected in a property?

Turn off appliances at their own controls and wait 30 minutes
Turn on extraction fans to clear the gas
Open windows only and call the landlord
Do not operate any switches, open windows and doors, turn off the gas at the meter if safe, get everyone out, and call 0800 111 999 (Correct answer)

Correct answer: Do not operate any switches, open windows and doors, turn off the gas at the meter if safe, get everyone out, and call 0800 111 999

On detecting a gas smell: do not operate any electrical switches (which can ignite gas), ventilate by opening windows and doors, turn off the gas at the emergency control valve (meter) if safe, evacuate, and call 0800 111 999 from outside.

Question 8: What are the recommended actions for a Gas Safe engineer if they detect high CO levels in a property?

Test the CO level with a monitor and leave if it is below 100 ppm
Evacuate the occupants immediately, ventilate, call 999 if anyone is affected, and do not restore gas until the source is identified and repaired (Correct answer)
Complete the work and advise the occupant to open windows
Only act if the CO level exceeds 1,000 ppm

Correct answer: Evacuate the occupants immediately, ventilate, call 999 if anyone is affected, and do not restore gas until the source is identified and repaired

High CO levels require immediate evacuation of all occupants, ventilation of the property, calling 999 if anyone shows symptoms (headache, nausea, dizziness), and not restoring gas until the source is identified and remedied.

Question 9: What is the maximum permissible pressure drop during a domestic gas tightness test using a water gauge or electronic manometer?

No drop is acceptable for a new installation — any pressure drop indicates a leak requiring investigation (Correct answer)
A small drop is expected due to temperature change and can be ignored
A drop of up to 0.5 mbar per hour is acceptable
A drop of up to 1 mbar is acceptable for all installations

Correct answer: No drop is acceptable for a new installation — any pressure drop indicates a leak requiring investigation

For a new gas installation, no pressure drop is acceptable. Any drop indicates a leak that must be traced and repaired. Temperature compensation must be applied for extended tests, but any residual drop indicates a fault.

Question 10: When carrying out a flue flow test (spillage test) on an open-flued appliance, where should the smoke match be held?

At the gas meter
At the base of the draught diverter or canopy (Correct answer)
At the flue terminal on the outside of the building
At the ventilation grille

Correct answer: At the base of the draught diverter or canopy

The smoke match or smoke pellet should be held at the base of the draught diverter or canopy of the appliance. The smoke should be drawn upwards into the flue if the flue is operating correctly. If the smoke spills outward into the room, it indicates that the flue is not drawing properly and combustion products may be entering the living space.

Question 11: What type of joint is NOT permitted for use on gas pipework concealed within a wall cavity?

Brazed joints
Compression joints (Correct answer)
Soldered capillary joints
Welded joints

Correct answer: Compression joints

Compression joints (and any other type of mechanical joint that could work loose) are not permitted on gas pipework that is to be concealed within wall cavities or where access is restricted. Only permanent joints such as soldered capillary, brazed, welded, or press-fit joints with appropriate certification for gas should be used in concealed locations.

Question 12: What is the purpose of a CO alarm in a domestic property?

CO alarms are only required in commercial properties
To automatically shut off gas appliances when CO is detected
To provide early warning of CO accumulation before dangerous concentrations are reached, allowing occupants to evacuate (Correct answer)
To measure the efficiency of gas appliances for service purposes

Correct answer: To provide early warning of CO accumulation before dangerous concentrations are reached, allowing occupants to evacuate

CO alarms provide an audible warning when CO concentrations rise, giving occupants time to evacuate before reaching dangerous levels. They are the only way to detect CO, which has no smell or colour.

Question 13: A gas engineer needs to check the standing pressure at a domestic meter. What reading should they expect under normal conditions?

21 mbar (Correct answer)
11 mbar
35 mbar
75 mbar

Correct answer: 21 mbar

The normal standing pressure (static pressure) at a domestic gas meter in the UK should be approximately 21 mbar. This is measured with all appliances turned off (no gas flowing). The working pressure (with appliances operating) should not drop below 19 mbar at the meter. A significant deviation may indicate a supply problem.

Question 14: When testing the combustion performance of a gas appliance, what does a high CO/CO₂ ratio indicate?

Excess air is entering the appliance
Incomplete combustion is occurring (Correct answer)
Perfect combustion conditions
The flue is working efficiently

Correct answer: Incomplete combustion is occurring

A high CO/CO₂ ratio indicates incomplete combustion. The acceptable maximum CO/CO₂ ratio for most appliances is 0.004 (or 1:250). A ratio exceeding this indicates that the appliance is producing dangerous levels of carbon monoxide relative to the carbon dioxide output, and the appliance requires investigation and rectification.

Question 15: What must an engineer check on the gas meter before commencing any work on a gas installation?

The meter serial number, ECV operation, and that the regulator is functioning correctly (correct standing and working pressures) (Correct answer)
The brand name of the meter
The colour of the meter casing
Whether the meter has been painted recently

Correct answer: The meter serial number, ECV operation, and that the regulator is functioning correctly (correct standing and working pressures)

Before starting work, an engineer must check the gas meter serial number, verify the ECV operates freely and fully closes (let-by test), confirm the meter regulator is delivering correct standing pressure (21 mbar with no load) and working pressure (minimum 19 mbar with all appliances on). This ensures the supply is safe and adequate before making any modifications.

Question 16: What is the purpose of the 'stabilisation period' at the start of a gas tightness test?

To allow the engineer time to leave the building safely
Stabilisation is not part of the standard tightness test procedure
To allow appliances to reach operating temperature before the test
To allow temperature and pressure to equalise after pressurising, preventing a false reading due to adiabatic heating of the compressed gas (Correct answer)

Correct answer: To allow temperature and pressure to equalise after pressurising, preventing a false reading due to adiabatic heating of the compressed gas

When gas is compressed into pipework during pressurisation, adiabatic heating temporarily raises the pressure. The stabilisation period allows the temperature — and therefore the pressure — to equalise before the test reading is taken.

Question 17: What should an engineer do if a gas appliance cannot achieve the correct working pressure during commissioning?

Do not commission the appliance and investigate the cause of the low pressure (Correct answer)
Inform the customer and leave the appliance in service at reduced input
Commission the appliance and note the pressure deficit in the paperwork
Adjust the appliance gas valve to compensate for the low pressure

Correct answer: Do not commission the appliance and investigate the cause of the low pressure

An appliance that cannot achieve its design working pressure must not be commissioned, as incorrect gas pressure leads to incomplete combustion, poor efficiency, and potentially dangerous operating conditions.

Question 18: When checking for gas leaks at a meter connection, which method should be used?

A thermal imaging camera
Approved leak detection fluid (LDF) applied to joints and connections (Correct answer)
A naked flame held close to the joint
Soapy water made from household washing-up liquid

Correct answer: Approved leak detection fluid (LDF) applied to joints and connections

Approved leak detection fluid (LDF) conforming to BS EN 14291 must be used to check for gas leaks at meter connections and joints. The fluid is applied to suspected leak points and will bubble if gas is escaping. Never use a naked flame to check for gas leaks. Household soap solutions may cause corrosion and are not suitable.

Question 19: When sleaving gas pipework through a wall, what must the sleeve extend to on each side?

At least 50 mm beyond the wall surface on the external side only
Flush with the wall surface on both sides (Correct answer)
The sleeve should be sealed at both ends
At least 25 mm beyond the wall surface on each side

Correct answer: Flush with the wall surface on both sides

When passing gas pipe through a wall, the sleeve must extend flush with the plaster or wall surface on each side. The gap between the pipe and the sleeve should be sealed at both ends with a suitable fire-resistant sealant to prevent gas migration through the wall cavity. The sleeve protects the pipe from corrosion where it passes through masonry.

Question 20: Why must flue terminals be correctly positioned on an external wall or roof?

Terminals must face north to prevent wind-induced back-draughts
Terminal positioning is only relevant for aesthetic reasons
Terminal position only matters for boilers over 20 kW output
To ensure adequate dispersion of flue gases away from windows, doors, and air vents, and to prevent re-entry of combustion products (Correct answer)

Correct answer: To ensure adequate dispersion of flue gases away from windows, doors, and air vents, and to prevent re-entry of combustion products

Flue terminals must be positioned to ensure combustion products disperse safely without re-entering the building through windows, doors, or ventilation openings. Document J of the Building Regulations specifies minimum clearance distances.

Question 21: Before commissioning a new gas appliance, what electrical checks must the engineer perform?

Confirm the circuit uses 2.5mm² cable throughout
Check that the appliance is correctly earthed and that polarity is correct (Correct answer)
Ensure a 30mA RCD protects the appliance circuit
Verify the supply voltage is exactly 230V

Correct answer: Check that the appliance is correctly earthed and that polarity is correct

The engineer must verify correct earthing and electrical polarity before commissioning any gas appliance with an electrical supply, as incorrect earthing or reversed polarity can create a serious safety hazard.

Question 22: What is the purpose of purging a gas installation after completing pipework installation or modification?

To remove air from the pipework and replace it with gas, preventing a potentially explosive air-gas mixture (Correct answer)
To test the tightness of the installation
To measure the gas flow rate
To check the burner pressure of connected appliances

Correct answer: To remove air from the pipework and replace it with gas, preventing a potentially explosive air-gas mixture

Purging removes the air from newly installed or modified gas pipework and replaces it with gas. This is essential because a mixture of air and gas within the pipe could form an explosive mixture. Purging must be carried out safely in accordance with IGE/UP/1B, ensuring proper ventilation and that no ignition sources are present.

Question 23: What safety feature prevents a gas appliance from operating if the fan in a fanned-flue system fails?

An air pressure switch (APS) that proves fan operation before allowing the gas valve to open (Correct answer)
The overheat thermostat
The timer programmer
The room thermostat

Correct answer: An air pressure switch (APS) that proves fan operation before allowing the gas valve to open

An air pressure switch (APS) is a safety device that detects whether the fan is running and creating sufficient draught before allowing the gas valve to open. If the fan fails to operate or cannot generate adequate pressure differential, the APS will not make and the gas valve will remain closed, preventing the burner from firing without a safe means of flue gas evacuation.

Question 24: Under GSIUR 1998, what must an employer ensure before allowing an employee to carry out gas work?

The employee holds a valid ACS certificate and is registered with Gas Safe (Correct answer)
The employee has at least 5 years of experience
The employee has completed a university degree in engineering
The employee is over 25 years of age

Correct answer: The employee holds a valid ACS certificate and is registered with Gas Safe

Under Regulation 3 of GSIUR 1998, employers must not allow employees to carry out gas work unless they are competent to do so. Competence is demonstrated through holding appropriate ACS (Accredited Certification Scheme) certificates, and the engineer must be registered on the Gas Safe Register.

Question 25: What is the function of a flame supervision device (FSD) on a gas appliance?

To shut off the gas supply to the burner if the flame is extinguished, preventing a gas escape (Correct answer)
To provide ignition sparks to the burner
To control the room temperature
To adjust the flame height for efficiency

Correct answer: To shut off the gas supply to the burner if the flame is extinguished, preventing a gas escape

A flame supervision device (FSD), such as a thermocouple, flame rectification probe, or mercury vapour capsule, monitors the presence of a flame at the burner. If the flame is extinguished for any reason, the FSD closes the gas valve to prevent unburnt gas from escaping into the room. This is a critical safety device on all modern gas appliances.

Question 26: What is the minimum free area of a permanent air vent required for a flueless gas appliance such as a cooker with a rated input of 15 kW?

Depends on the room volume only
5 cm² per kW of rated input above 7 kW
No ventilation required below 20 kW
5 cm² per kW of rated net input (Correct answer)

Correct answer: 5 cm² per kW of rated net input

Flueless appliances require ventilation of 5 cm² of free area per kW of rated net input for the total input of the appliance (not just the amount above 7 kW as with open-flued appliances). For a 15 kW flueless appliance, this would require 75 cm² of free area ventilation.

Question 27: What safety precaution is taken after purging gas into the atmosphere outside?

Confirm the purge point is clear of ignition sources, the gas is fully dispersed before any ignition sources are introduced, and the area is ventilated (Correct answer)
Allow immediate reoccupation of the building
Apply a pressure test immediately after purging
Light a match at the purge point to confirm gas is present

Correct answer: Confirm the purge point is clear of ignition sources, the gas is fully dispersed before any ignition sources are introduced, and the area is ventilated

After purging gas to atmosphere, the purge point and nearby area must be kept clear of ignition sources until the gas has fully dispersed. Good ventilation speeds dispersal. Only when gas is confirmed to have dispersed should ignition sources be reintroduced.

Question 28: Which part of the Building Regulations covers the installation of combustion appliances in England?

Part J — Combustion Appliances and Fuel Storage Systems (Correct answer)
Part L — Conservation of Fuel and Power
Part E — Resistance to Sound
Part P — Electrical Safety

Correct answer: Part J — Combustion Appliances and Fuel Storage Systems

Approved Document J of the Building Regulations covers the requirements for combustion appliances and fuel storage systems, including gas appliances. It addresses air supply, discharge of combustion products, protection of buildings, and provision of information.

Question 29: If a Gas Safe engineer arrives at a property and finds a CO alarm sounding, what is the correct immediate action?

Assume the alarm is faulty and reset it
Turn off the CO alarm and investigate the appliance
Check the appliance before evacuating to confirm CO is actually present
Evacuate occupants, ventilate the property, do not operate any electrical switches, and call 999 if anyone shows symptoms (Correct answer)

Correct answer: Evacuate occupants, ventilate the property, do not operate any electrical switches, and call 999 if anyone shows symptoms

A sounding CO alarm must be treated as a real emergency. Evacuate all occupants, ventilate, avoid electrical switches, and call 999 if anyone is symptomatic. Do not waste time checking whether the alarm is genuine before evacuating.

Question 30: What is the correct working gas pressure for natural gas at a domestic appliance inlet, measured while the appliance is operating at full load?

20 mbar (Correct answer)
21 mbar
17 mbar
25 mbar

Correct answer: 20 mbar

The working pressure for natural gas at a domestic appliance inlet should be 20 mbar when measured with the appliance operating at full load, slightly below the 21 mbar standing pressure.

Question 31: What dangerous gas is produced as a result of incomplete combustion of natural gas?

Carbon monoxide (CO) (Correct answer)
Sulphur dioxide (SO₂)
Nitrogen dioxide (NO₂)
Carbon dioxide (CO₂)

Correct answer: Carbon monoxide (CO)

Carbon monoxide (CO) is a highly toxic, colourless, and odourless gas produced when natural gas undergoes incomplete combustion due to insufficient oxygen supply. CO poisoning can be fatal. Signs of incomplete combustion include yellow or orange flames, sooting, and increased CO/CO₂ ratios.

Question 32: What type of flue system draws combustion air from the room and discharges products of combustion to the outside?

Room-sealed flue (Type C)
Forced draught flue (Type D)
Flueless (Type A)
Open flue (Type B) (Correct answer)

Correct answer: Open flue (Type B)

An open flue (Type B) system draws its combustion air from the room in which the appliance is installed and discharges the products of combustion to the outside through a flue pipe and terminal. Because it takes air from the room, adequate permanent ventilation must be provided to replace the air consumed.

Question 33: What is the minimum distance a room-sealed balanced flue terminal must be from an openable window or air vent?

300mm (Correct answer)
600mm
150mm
1200mm

Correct answer: 300mm

BS 5440 Part 1 requires a room-sealed appliance flue terminal to be at least 300mm from any openable window, air vent, or opening to prevent combustion products from re-entering the building.

Question 34: What is the function of a flue gas analyser when commissioned or servicing a gas appliance?

It tests the mechanical strength of the flue components
It detects gas leaks in the flue pipework
It measures the gas pressure in the flue
It measures the composition of flue gases (CO, CO2, O2) to confirm complete combustion and identify potential problems (Correct answer)

Correct answer: It measures the composition of flue gases (CO, CO2, O2) to confirm complete combustion and identify potential problems

A flue gas analyser measures the percentage of CO, CO2, and O2 in the flue gases. The results confirm whether combustion is complete and efficient. Abnormal readings indicate combustion problems requiring investigation.

Question 35: What pipe sizing consideration is critical to ensure correct gas appliance operation?

Pipe size is only relevant for commercial installations
Pipe sizing only affects the time taken to purge the system
Oversized pipes always improve appliance performance
The pipe must be sized to deliver the required gas flow rate (volume) without excessive pressure drop — undersized pipes starve appliances of gas (Correct answer)

Correct answer: The pipe must be sized to deliver the required gas flow rate (volume) without excessive pressure drop — undersized pipes starve appliances of gas

Gas pipes must be sized to deliver adequate gas volume to all appliances simultaneously at the required pressure. Undersized pipes cause excessive pressure drop, starving appliances of gas and causing incomplete combustion.

Question 36: What is the significance of CO (carbon monoxide) in the context of gas emergencies?

CO is only dangerous outdoors
CO has a distinctive smell that warns occupants before dangerous levels are reached
CO is only produced by malfunctioning appliances — a serviced appliance cannot produce CO
CO is colourless and odourless, highly toxic even in small concentrations, and can rapidly cause loss of consciousness and death (Correct answer)

Correct answer: CO is colourless and odourless, highly toxic even in small concentrations, and can rapidly cause loss of consciousness and death

CO is colourless and odourless, making it undetectable without a CO alarm. It combines with haemoglobin in the blood far more readily than oxygen, rapidly causing incapacitation and death even at relatively low concentrations.

Question 37: What special precaution must be taken before re-entering a property after a gas escape has been reported?

Re-entry is permitted once 30 minutes have elapsed after the escape
The gas network operator's engineer must have confirmed it is safe to re-enter and the gas supply has been isolated or the fault repaired (Correct answer)
Only the police can authorise re-entry after a gas escape
Re-entry is the occupant's own decision

Correct answer: The gas network operator's engineer must have confirmed it is safe to re-enter and the gas supply has been isolated or the fault repaired

A property must not be re-entered after a gas escape until the gas network operator's engineer (or Gas Safe engineer if appropriate) has confirmed the gas supply is isolated or the fault repaired and the property is safe.

Question 38: When installing a vertical flue from a gas boiler through a flat roof, what is the minimum height the flue terminal must extend above the roof surface?

600 mm (Correct answer)
150 mm
At least 250 mm above the highest point of the roof penetration
300 mm

Correct answer: 600 mm

A vertical flue terminal passing through a flat roof must extend at least 600 mm above the roof surface. This height ensures adequate dispersal of combustion products, prevents the terminal from being blocked by debris or ponding water, and reduces the risk of flue gases being drawn back into the building through nearby openings.

Question 39: What is the purpose of a gas meter bypass?

It allows gas to continue during meter maintenance
It is a safety valve that diverts gas during excess pressure events
It is a pressure regulator fitted parallel to the meter
It is not a legitimate installation component — a bypass around a gas meter is illegal as it allows gas use without metering (Correct answer)

Correct answer: It is not a legitimate installation component — a bypass around a gas meter is illegal as it allows gas use without metering

There is no legitimate purpose for a bypass around a gas meter in a domestic installation. Creating or using a meter bypass is a criminal offence as it enables theft of gas and creates serious safety risks.

Question 40: What is the standard working pressure for natural gas supplied to domestic properties in the UK?

75 mbar
21 mbar (Correct answer)
35 mbar
11 mbar

Correct answer: 21 mbar

The standard working pressure for natural gas in UK domestic properties is 21 mbar (approximately 8.4 inches water gauge). This is the nominal pressure maintained by the gas distribution network at the meter outlet. Engineers must verify this pressure when commissioning or servicing appliances.

Question 41: What is the purpose of the Gas Industry Unsafe Situations Procedure (GIUSP)?

To manage customer complaints about gas bills
To regulate the manufacture of gas appliances
To provide a standardised procedure for engineers when they encounter unsafe gas installations (Correct answer)
To set pricing standards for gas work

Correct answer: To provide a standardised procedure for engineers when they encounter unsafe gas installations

The Gas Industry Unsafe Situations Procedure (GIUSP) provides a standardised framework for Gas Safe registered engineers to classify and deal with unsafe gas installations. It categorises situations as Immediately Dangerous (ID), At Risk (AR), or Not to Current Standards (NCS), with specific actions required for each classification.

Question 42: What material is commonly used for flexible flue liners in gas installations within masonry chimneys?

Aluminium alloy
316 grade stainless steel (Correct answer)
Plastic PVC
Galvanised mild steel

Correct answer: 316 grade stainless steel

316 grade stainless steel is the standard material for flexible flue liners used in gas installations within masonry chimneys. It provides excellent resistance to the corrosive condensates produced by gas combustion and has the durability required for the expected lifespan of the installation. It must conform to BS EN 1856-2.

Question 43: What is the minimum free area of ventilation required for an open-flued gas appliance with a rated input over 7 kW in a room?

5 cm² per kW of rated input above 7 kW (Correct answer)
10 cm² per kW of rated input above 7 kW
5 cm² for every kW of rated input
No additional ventilation is required

Correct answer: 5 cm² per kW of rated input above 7 kW

For open-flued appliances with a rated input exceeding 7 kW, additional ventilation of 5 cm² of free area per kW above 7 kW is required. The first 7 kW is considered to be served by normal air infiltration in the room. This is specified in BS 5440-2 and Approved Document J.

ACS CCN1 Core Domestic Gas Safety Assessment

The ACS CCN1 is the UK's core domestic gas safety certification required for Gas Safe Register membership. It covers gas legislation, combustion, ventilation, pipework, flue systems, unsafe situations procedures, and meter controls through written multiple-choice assessments.

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