The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, (51) this is largely because, unlike animals, we stand upright. This means that our noses are (52) to perceiving those smells which float through the air, missing the majority of smells which stick to surfaces. In fact, (53) , we are extremely sensitive to smells, even if we do not generally realize it. Our noses are capable of (54) human smells 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, (55) others are sensitive to the smells of both flowers. This may be because some people do not have the genes necessary to generate (56) smell receptors in the nose. These receptors are the cells which sense smells and send (57) 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 (58) to it often enough.
The explanation for insensitivity to smell seems to be that the brain finds it (59) to keep all smell receptors working all the time but can (60) new receptors if necessary.
52().
A.limited
B.committed
C.dedicated
D.confined
参考答案：A
解析：
A．1imited：限制。B．committed：犯(错误)，干(坏事)，把……交托给，提交，答应负责。C．dedicated：献(身)，致力，题献(一部著作给某人)。D．confined：限制，禁闭，界限，边界。强干扰项是D选项。limit，confine这二个动词的一般含义为“限制”或“局限”。limit指时空、程度、量等方面的“限定”，其内涵是如果超出了这种限度就会受罚或遭到令人不快的后果；此外，这个词也常用来表示“局限”；confine具有limit和restrict两者的含义，但confine的内涵是“约束”或“束缚”。联系原文，文章是在说数量上的限制，人类的鼻子的功能仅限于某些方面，故A选项为正确答案。