Meaning: 'Survive' means to continue to live or exist, especially in difficult conditions, which is relevant to how polar bears thrive in the Arctic.

Wrong options:

• tend: The verb 'tend' implies care or attention, which does not fit the context of enduring harsh conditions.
• stretch: The verb 'stretch' refers to extending something physically, which is unrelated to the survival of polar bears in extreme environments.
• confirm: The verb 'confirm' means to establish the truth or correctness of something, which does not relate to the ability of polar bears to live in harsh conditions.

Correct answer: mimics

Explanation: The verb 'mimics' is appropriate as it indicates that the synthetic fibre imitates the properties of polar bear fur, fitting both grammatically and contextually within the sentence.

Meaning: 'Mimics' means to imitate or replicate, which in this context refers to the synthetic fibre copying the characteristics of polar bear fur.

Wrong options:

• calculates: The verb 'calculates' refers to determining a numerical value, which does not apply to the properties of fur.
• pastes: The verb 'pastes' means to attach something using an adhesive, which is irrelevant in this context of imitation.
• requests: The verb 'requests' means to ask for something, which does not fit the context of describing the properties of the fibre.

Correct answer: much

Explanation: The adverb 'much' is correctly used here to indicate a significant degree of difference, fitting grammatically and contextually to describe the comparative thickness of the fibre.

Meaning: 'Much' is used to indicate a large amount or degree, in this case, referring to the fibre being thinner than down feather.

Wrong options:

• more: The adverb 'more' is comparative but does not fit correctly in this context as it lacks the necessary degree modifier for the comparison being made.
• too: The adverb 'too' implies an excessive degree, which does not fit the intended meaning of simply being thinner.
• such: The adverb 'such' is used to indicate a type or kind, which does not appropriately convey the comparative aspect needed here.

Correct answer: convinced

Explanation: The verb 'convinced' fits grammatically and contextually as it indicates that some experts are not persuaded by the researchers' claims, aligning with the overall sentiment of skepticism expressed in the passage.

Meaning: 'Convinced' means to be persuaded or assured about something, which in this case refers to experts' belief in the researchers' claims.

Wrong options:

• preferred: The verb 'preferred' indicates a choice or liking, which does not relate to the experts' belief in the claims.
• refused: The verb 'refused' means to decline or reject, which does not accurately capture the experts' stance of skepticism.
• suspected: The verb 'suspected' implies doubt or mistrust, but does not convey the idea of being unconvinced as effectively as 'convinced' does.

Correct answer: verify

Explanation: The verb 'verify' is appropriate as it indicates the need to confirm the accuracy of the fibre's advantages, fitting grammatically and contextually within the sentence.

Meaning: 'Verify' means to confirm the truth or accuracy of something, which is relevant to the need for further research on the fibre's benefits.

Wrong options:

• expose: The verb 'expose' means to reveal or uncover, which does not fit the context of confirming advantages.
• appear: The verb 'appear' suggests something is seen or seems to be, which does not convey the action of confirming or validating.
• consent: The verb 'consent' means to agree or give permission, which is unrelated to the context of verifying claims.