单选题
The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, but this is largely because, unlike animals, we stand upright. This means that our noses are 35 to perceiving those smells which float through the air, missing the majority of smells which stick to surfaces. In fact, though, we are 36 sensitive to smells, even ff we do not generally realize it. Our noses are capable of 37 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 38 smell receptors in the nose. These receptors are the cells which sense smells and send 39 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 40 to it often enough. The explanation for insensitivity to smell seems to be that the brain finds it 41 to keep all smell receptors working all the time but can create new receptors if necessary. This may also explain why we are not usually sensitive to our own smells—we 42 do not need to be. We are not 43 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 44 signals such as the smell of smoke, which might indicate the danger of fire. A. simply E. permanently I. dedicated M. distinguishing B. emergency F. limited J. exposed N. particular C. aware G. sure K. impulses O. extremely D. detecting H. inefficient L. messages
【答案解析】空格前的of是介词，其后应该填入动名词与后面的human smells构成动宾搭配，即“我们的鼻子可以______人类的气昧”。本段讨论的是人类鼻子对气味的敏感度，上文出现了sensitive to smells，故推测此处应该填表示“闻到或察觉”之类的词语。detecting强调察觉不易察觉的事物，符合句意。M项distinguishing常指通过视觉或听觉来识别事物，不能与smells搭配。