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  3. The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, but this is lar

The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, but this is lar

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问题     The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, but this is largely because, unlike animals, we stand upright This means that our noses are 【C1】______ to perceiving those smells which float through the air, missing the majority of smells which stick to surfaces. In fact, though, we are【C2】______ sensitive to smells, even if we do not generally realize it. Our noses are capable of【C3】______ human smells even when these are diluted to far below one part in one million.
    Strangely, some people find that they can smell one type of flower but not another, whereas others are sensitive to the smells of both flowers. This may be because some people do not have the genes necessary to generate【C4】______ smell receptors in the nose. These receptors are the cells which sense smells and send【C5】______ to the brain. However, it has been found that even people insensitive to a certain smell at first can suddenly become sensitive to it when【C6】______ to it often enough.
    The explanation for insensitivity to smell seems to be that the brain finds it【C7】______ to keep all smell receptors working all the time but can create new receptors if necessary. This may also explain why we are not usually sensitive to our own smells—we【C8】______ do not need to be. We are not【C9】______ 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 available for unfamiliar and【C10】______ signals such as the smell of smoke, which might indicate the danger of fire.
A) simply E) permanently I) dedicated M) distinguishing
B) emergency F) limited J) exposed N) particular
C) aware G) sure K) impulses 0) extremely
D) detecting H) inefficient L) messages
【C5】
选项
答案L
解析 空格所在句是which引导的定语从句，填入的词作send的宾语。messages指“信息”，这里指感受器把信息传给大脑，符合句子逻辑。impulses多表示人的冲动或兴奋，用在此处不合适。
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