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.
【C1】
选项 A、Although
B、as
C、but
D、while
答案C
解析 句意“人们常常认为，与动物相比，人类的嗅觉不够敏锐，……而这在很大程度上是因为人类直立行走，这一点与动物……。”although表示让步；as表示时间或者原因；but表示转折关系；while表示时间或者对比。四个选项中，but是表示转折的并列连诃，but后面的内容是语句重心所在。while也可以表示对比、转折，但作为从属连词也有让步含义。从本题前后的语意关系来看，后半句语义应当是重心所在。故答案为c。
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