Meaning: 'Reintroducing' means to bring something back into a place where it was previously present, in this case, wolves into the park.

Wrong options:

• correlated: Correlated is an adjective that describes a relationship between two things, which does not fit as a subject in this context.
• feeding: Feeding is a gerund that implies providing food, which does not relate to the action of bringing wolves back.
• using: Using is a gerund that indicates employing something, which does not fit the context of reintroducing wolves.
• used: Used is the past tense of use, which does not fit grammatically as it does not serve as a subject here.
• avoiding: Avoiding is a gerund that indicates the action of staying away from something, which does not fit as the main action being discussed.
• claimed: Claimed is the past tense of claim, which does not fit as it does not serve as a subject in this context.

Correct answer: correlated

Explanation: The term 'correlated' is an adjective that describes the relationship between the reintroduction of wolves and the growth of willow and cottonwood. It fits grammatically as it describes how the two actions are related in the context of the study.

Meaning: 'Correlated' means that there is a mutual relationship or connection between two or more things, indicating that one may influence the other.

Wrong options:

• reintroducing: Reintroducing is a gerund that serves as the subject of the previous clause, which does not fit here as it does not describe a relationship.
• avoiding: Avoiding is a gerund that indicates the action of staying away from something, which does not fit the context of describing a relationship.
• feeding: Feeding is a gerund that implies providing food, which does not relate to the relationship being described.
• using: Using is a gerund that indicates employing something, which does not fit the context of correlation.
• used: Used is the past tense of use, which does not fit grammatically as it does not describe a relationship.

Correct answer: avoiding

Explanation: The word 'avoiding' is a gerund that describes the action of the grazing animals in relation to the sites. It fits grammatically as it serves as the subject of the clause, indicating what the elk were doing in response to the presence of wolves.

Meaning: 'Avoiding' means to stay away from something, in this case, the sites where they could not easily escape.

Wrong options:

• correlated: Correlated is an adjective that describes a relationship and does not fit as an action performed by the elk.
• feeding: Feeding is a gerund that implies providing food, which does not relate to the action of the elk in this context.
• using: Using is a gerund that indicates employing something, which does not fit the context of the elk's behavior.
• reintroducing: Reintroducing is a gerund that refers to the action of bringing wolves back, which does not describe the elk's actions.
• claimed: Claimed is the past tense of claim, which does not fit as it does not describe an action performed by the elk.

Correct answer: claimed

Explanation: The word 'claimed' is the past tense of the verb 'claim' and serves as the main verb of the clause. It fits grammatically as it indicates what the scientists did in response to their findings about the wolves and the vegetation.

Meaning: 'Claimed' means to assert or state something as a fact, in this case, what the scientists concluded about the relationship between wolves and plant growth.

Wrong options:

• reintroducing: Reintroducing is a gerund that does not fit as a main verb in this context.
• correlated: Correlated is an adjective that describes a relationship and does not fit as a verb in this context.
• avoiding: Avoiding is a gerund that indicates an action but does not serve as the main verb in this clause.
• feeding: Feeding is a gerund that implies providing food, which does not fit as a main verb here.
• using: Using is a gerund that indicates employing something, which does not fit as a main verb in this context.