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

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

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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,【C1】________ animals, we stand upright. This means that our noses are limited to perceiving those smells which float through the air,【C2】________the majority of smells which stick to surfaces. In fact, though, we are extremely sensitive to smells,【C3】________we do not generally realize it. Our noses are capable of detecting human smells even when these are【C4】________ 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【C5】________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【C6】________can suddenly become sensitive to it when exposed to it often enough.
    The explanation for insensitivity to smell seems to be that brain finds it【C7】________to keep all smell receptors working all the time but can create new receptors if necessary. This may【C8】________ explain why we are not usually sensitive to our own smells — we simply do not need to be. We are not aware of the usual smell of our own house, but we【C9】________new smells when we visit someone else’ s. The brain finds it best to keep smell receptors available for unfamiliar and emergency signals【C10】________ the smell of smoke, which might indicate the danger of fire.
【C3】
选项 A、even if
B、if only
C、only if
D、as if
答案A
解析 空格后面的it指代前面的we are extremely sensitive to smells，即“事实上我们对气味非常敏感，________我们通常没有意识到这一点。”由此可以确定，该空格处应该填入一个表示转折或让步关系的词。四个选项中只有A选项even if“即使，虽然”可以表示让步关系，故选A。B选项if only“但愿……该多好啊，要是……就好了”，常用于虚拟语气。C选项only if“只有，只要”，表示条件关系。D选项as if“好像”常用于引导方式状语从句。
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