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.
【C4】
选项 A、diluted
B、dissolved
C、dispersed
D、diffused
答案A
解析 空格所在句的句意是：即使人类的气味被________到百万分之一以下，我们的鼻子也能捕捉到这些气味。A选项diluted“冲淡，稀释”，可以用在液体或气体的稀释上，指“减少某物的强度、浓度、纯度”，符合语义逻辑，而且可以后接百分比表示稀释的程度，故选A。B选项dissolved“溶解”，C选项dispersed“分散”，D选项diffused分散，传播”，均不符合文章语义逻辑，均可排除。
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