2. 考研
  3. The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals,【C1】______this i

The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals,【C1】______this i

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问题     The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals,【C1】______this is largely because, 【C2】______animals, we stand upright. This means that our noses are【C3】______to perceiving those smells which float through the air, 【C4】______the majority of smells which stick to surfaces. In fact, 【C5】______, we are extremely sensitive to smells, 【C6】______we do not generally realize it. Our noses are capable of 【C7】______human smells even when these are【C8】______to far below one part in one million.
    Strangely, some people find that they can smell one type of flower but not another, 【C9】______others are sensitive to the smells of both flowers. This may be because some people do not have the genes necessary to generate【C10】______smell receptors in the nose. These receptors are the cells which sense smells and send messages to the brain. However, it has been found that even people insensitive to a certain smell【C11】______can suddenly become sensitive to it when exposed to it often enough.
    The explanation for insensitivity to smell seems to be that the brain finds it【C12】______to keep all smell receptors working all the time but can create new receptors if necessary. This may 【C13】______explain why we are not usually sensitive to our own smells—we simply do not need to be. We are not【C14】______of the usual smell of our own house, but we notice new smells when we visit someone else’s. The brain finds it best to keep smell receptors【C15】______for unfamiliar and emergency signals such as the smell of smoke, which might indicate the danger of fire.
【C11】
选项 A、at first
B、at all
C、at large
D、at times
答案A
解析 句意“然而，……对某种特定气味不敏感的人也能突然变得敏感起来。”在本句中，供选的状语修饰整个句子。选项A．at first起初；B．at all根本；C．at large全面地，详细地，无拘无束地；D．at times有时。由于谓语部分的频度状语“突然”体现了时间的交替关系，句子应该表达起初不敏感。故答案为A。
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