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.
【C11】

选项 A、signs
B、stimuli
C、messages
D、impulses

答案C

解析 语义衔接题。which引导定语从句,修饰cells,说明这些细胞的功能,从句中and连接两个并列谓语sense和send。本句是说这些感应器是一些细胞,这些细胞能够感应气味并把______发送到大脑,所填词应与send构成动宾搭配。从句意来看,向大脑发送的应该是细胞所感应到的气味的信息,messages(消息,音信)符合此处语义要求,故为答案。signs意为“痕迹,征兆,表象”与messages近义,为强干扰项,但不能与send构成动宾搭配,故排除。stimuli(刺激物,促进因素)和impulses(冲动,一时兴起的念头)均不能使此处语义通顺,故排除。
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