TOEFL Practice Test #8

Question 1

______ aluminum is exposed to oxygen, a tough, invisible oxide forms, making it extremely corrosion-resistant.

Accepted Answer

Once

Answer

The word 'Once' correctly introduces a condition that, when met, triggers a specific outcome. The sentence describes that *as soon as* or *when* aluminum is exposed to oxygen, a protective oxide layer forms. 'Once' establishes this immediate cause-and-effect relationship, making it the most appropriate conjunction to link the exposure to the resulting formation of the oxide.

Question 2

______ the Silurian Period, there was significant radiation of rapacious fish equipped with bulky jaws.

Accepted Answer

During

Answer

The preposition 'During' is used to indicate that an event or action takes place within a specific period of time. Here, the 'significant radiation of rapacious fish' occurred within the timeframe of 'the Silurian Period.' This makes 'During' the correct choice to specify when this evolutionary event happened.

Question 3

Sickle-cell anemia, which is a genetic defect, is caused by ____ that encourages a faulty form of hemoglobin.

Accepted Answer

a certain mutant allele

Answer

This question tests the correct order of adjectives before a noun. The standard English adjective order is typically article + opinion/size/age/shape/color/origin/material + noun. In this case, 'a' is the article, 'certain' and 'mutant' are descriptive adjectives, and 'allele' is the noun. Therefore, 'a certain mutant allele' follows the correct grammatical structure.

Question 4

Mary McLeod Bethune, a leading African-American _____, as a child attended the local free school.

Accepted Answer

educator

Answer

The sentence uses an appositive phrase to provide additional information about Mary McLeod Bethune. An appositive is a noun or noun phrase that renames or clarifies another noun right beside it. 'Educator' is the correct noun form to function as an appositive, describing her profession without introducing unnecessary clauses or pronouns.

Question 5

Beryllium is used as a bonding agent for nuclear fuel elements ____ toughness and excellent resistance to heat.

Accepted Answer

because of its

Answer

The phrase 'because of its' correctly introduces a reason or cause, followed by a noun phrase. In this sentence, beryllium is used as a bonding agent *because of* its inherent qualities of 'toughness and excellent resistance to heat.' This construction clearly explains the justification for its use.