The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, 【C1】______ this

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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【C11】______ to the brain. However, it has been found that even people insensitive to a certain smell【C12】______can suddenly become sensitive to it when【C13】______ to it often enough.
    The explanation for insensitivity to smell seems to be that brain finds it【C14】______to keep all smell receptors working all the time but can【C15】______new receptors if necessary. This may 【C16】______explain why we are not usually sensitive to our own smells we simply do not need to be. We are not【C17】______of the usual smell of our own house but we【C18】______ new smells when we visit someone else’s. The brain finds it best to keep smell receptors【C19】______for unfamiliar and emergency signals【C20】______the smell of smoke, which might indicate the danger of fire.
【C13】

选项 A、subjected
B、left
C、drawn
D、exposed

答案D

解析 语义衔接题。横线所在部分为省略了主语they和be动词are的状语从句。其中,it指代前面的a certain smell,they指代people…at first,所填动词应与they构成动宾搭配,且后面能接to it。另外,此处阐述的是这些人由对某些气味不敏感变为敏感的条件:当这些人经常______ 这种气味时。exposed(暴露)代入句中,they are exposed to it...搭配合理,且“这些人经常被暴露于该种气味当中,即经常接触该种气味”能成为这些人对该气味敏感的条件,故答案为[D]项。be subjected to(经受,遭受)和be left to(被留交;遗赠)与smell语义不匹配,故均排除。be drawn to (被吸引)代入句中,“当这些人经常被吸引到该气味那里去”语义也不通,前面说对这些气味不敏感、闻不到,如何会被吸引呢?故排除。
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