2. 外语
  3. A. limited B. distinguish C. unlike D. particular E. trigger F. inefficient G. create H. emergency I. incompetent J. detecting K

A. limited B. distinguish C. unlike D. particular E. trigger F. inefficient G. create H. emergency I. incompetent J. detecting K

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问题 A. limited B. distinguish C. unlike D. particular E. trigger
F. inefficient G. create H. emergency I. incompetent J. detecting
K. aware L. messages M. unusual N. surfaces O. confined
   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【C2】______ to perceiving those smells which float through the air, missing the majority of smells which stick to【C3】______. In fact, though, we are extremely sensitive to smells, even if we do not generally realize it. Our noses are capable of【C4】______ 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【C5】______ smell receptors in the nose. These receptors are the cells which sense smells and send【C6】______ 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 exposed 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【C8】______ new receptors if necessary. This may also explain why we are not usually sensitive to our own smells-we simply 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.
【C3】
选项
答案N
解析 空格前的stick to表明，此处填入名词。本句说明的是人类的鼻子能够感受到的和不能闻到的气味，由此可推断此处填入的词要与前面的float through the air相反。surface“表面”符合语义。
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