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

Wrong options:

• reinforcing: 'Reinforcing' means to strengthen or support, which does not fit the context of bringing wolves back into the park.
• reforming: 'Reforming' implies making changes to improve something, which is not the action being described here.
• retrofitting: 'Retrofitting' refers to adding new technology or features to existing systems, which is unrelated to the ecological context of wolves.

Correct answer: correlated

Explanation: The word 'correlated' is the correct choice as it indicates a relationship between the reintroduction of wolves and the growth of plants, fitting grammatically as a past participle that describes the relationship established in the study.

Meaning: 'Correlated' means that two things are related or connected in some way, suggesting that the presence of wolves is linked to the growth of willow and cottonwood.

Wrong options:

• concentrated: 'Concentrated' means focused or gathered in one area, which does not accurately describe the relationship being discussed.
• corrosive: 'Corrosive' refers to something that causes damage or deterioration, which is not relevant to the context of ecological growth.
• collected: 'Collected' implies gathering or accumulating, which does not fit the context of establishing a relationship between wolves and plant growth.

Correct answer: avoiding

Explanation: The word 'avoiding' is appropriate as it describes the behavior of grazing animals in relation to the presence of wolves, fitting grammatically as a present participle that indicates ongoing action.

Meaning: 'Avoiding' means staying away from something, in this case, the sites where they could be easily preyed upon by wolves.

Wrong options:

• hiding: 'Hiding' suggests a passive action of concealing oneself, which does not convey the active behavior of avoiding danger.
• picking: 'Picking' implies selecting or choosing, which does not relate to the context of animal behavior in response to predators.
• presenting: 'Presenting' means to show or offer, which is not relevant to the context of animal behavior regarding safety.

Correct answer: claimed

Explanation: The word 'claimed' fits grammatically as a past tense verb that indicates what the scientists asserted regarding their findings, maintaining the narrative flow of the text.

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

Wrong options:

• shouted: 'Shouted' implies a loud vocalization, which does not fit the formal context of scientific reporting.
• published: 'Published' refers to making something publicly available, which does not convey the assertion made by the scientists in this context.
• spoke: 'Spoke' is a general term for verbal communication and lacks the specificity of asserting a claim.

Correct answer: expanded

Explanation: The word 'expanded' is the correct choice as it is a past tense verb that describes the growth of beaver colonies, fitting grammatically and contextually within the narrative of ecological changes following the wolves' reintroduction.

Meaning: 'Expanded' means to increase in size or scope, indicating that beaver colonies grew as a result of the changes in the ecosystem.

Wrong options:

• expansion: 'Expansion' is a noun and does not fit grammatically as a verb in this context.
• expanding: 'Expanding' is a present participle that does not match the past tense narrative of the sentence.
• expending: 'Expending' means to use up resources, which is unrelated to the context of growth in beaver colonies.