CBE - Certified Blockchain Expert Smart Contracts and DApps Questions and Answers

Question 1

A development team is building a decentralized application (DApp) for supply chain management.
The DApp needs to automatically trigger a payment to a supplier once a shipment's arrival is confirmed by an external logistics provider's API.
What component is essential for the smart contract to securely interact with this off-chain data?

Accepted Answer

A blockchain oracle.

Answer

A decentralized file storage system like IPFS.

Answer

The Ethereum Virtual Machine (EVM).

Answer

An integrated development environment (IDE) like Remix.

Question 2

Which of the following is a primary characteristic that distinguishes a smart contract from a traditional legal contract?

Accepted Answer

Its terms are self-executing and enforced by code on a blockchain.

Answer

It is written in a natural, human-readable language.

Answer

It relies on a central authority or legal system for enforcement.

Answer

It can be easily amended by any party after it has been agreed upon.

Question 3

A developer is writing a Solidity smart contract that handles user withdrawals. They write the code to send the Ether to the user's address *before* updating the user's balance in the contract's state. This sequence of operations makes the contract vulnerable to which specific type of attack?

Accepted Answer

Reentrancy

Answer

Integer Overflow

Answer

Denial of Service (DoS)

Answer

Timestamp Dependence

Question 4

What is the fundamental role of the backend in a typical Decentralized Application (DApp) architecture?

Accepted Answer

To run on a decentralized peer-to-peer network, typically consisting of smart contracts.

Answer

To host the user interface and frontend code on a centralized server.

Answer

To store large files and user data in a traditional SQL database.

Answer

To handle user authentication through a centralized identity provider.

Question 5

A financial DApp allows users to lend and borrow assets. The interest rates for these loans must be adjusted based on real-world market data. Which of the following is NOT a primary component needed to build this DApp?

Accepted Answer

A centralized server to store all transaction history for faster queries.

Answer

Smart contracts to manage the logic of lending and borrowing.

Answer

A frontend user interface for users to interact with the application.

Answer

An oracle to feed real-time asset prices into the smart contracts.

Question 6

When deploying a smart contract to the Ethereum network, what is the primary purpose of 'gas'?

Accepted Answer

To pay for the computational effort required to execute operations and record transactions on the blockchain.

Answer

A token used for governance votes within the DApp.

Answer

A fixed fee paid to the developers of the Solidity language.

Answer

A unit of data storage for the smart contract's variables.