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.
【C16】

选项 A、still
B、also
C、otherwise
D、nevertheless

答案B

解析 逻辑衔接题。this指代上句的that从句the brain…necessary,而该从句在上句中是在解释为什么人们对某些气味不够敏感。本句承接上句,说这解释了我们为什么通常对自己的气味不敏感,上句解释过一个了,这句又可以解释一个,可见本句与上句之间成递进关系,这既解释了……,也解释了……,also意为“而且(也),此外(还)”,表示递进,符合此处的逻辑要求,故为答案。still(还是,仍然)表示转折,otherwise(否则,不然)表示选择,nevertheless(仍然,然而,不过)表示转折,三者均不符合此处的逻辑要求,故均排除。
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