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.
【C5】

选项 A、unusual
B、particular
C、unique
D、typical

答案B

解析 空格所在句是在解释第二段第一句中提到的现象。首句中所提及的现象可能是因为缺少某种基因,所以无法在鼻子里生成某些气味的感受器,从而造成只能闻出一种花香而不能闻出另一种。也就是说,要闻出某种花香,鼻子里需要有某种“特定的”感受器。因此,B选项particular“特定的,特指的”符合文意,故选B。unusual“不平常的,与众不同的”,unique“独特的,唯一的”,typical“典型的”,均不符合文章语义逻辑,均可排除。
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