I. Use of English (Cloze)
The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals,___1___this is largely because,___2___animals, we stand upright. This means that our noses are___3___to perceiving those smells which float through the air,___4___the majority of smells which stick to surfaces. In fact,___5 ___ , we are extremely sensitive to smells,___6___we do not generally realize it. Our noses are capable of___7___human smells even when these are ___8___to far below one part in one million.
Strangely, some people find that they can smell one type of flower but not another,___9___others are sensitive to the smells of both flowers. This may be because some people do not have the genes necessary to generate___10___ smell receptors in the nose. These receptors are the cells which sense smells and send___11___to the brain. However, it has been found that even people insensitive to a certain smell___12___can suddenly become sensitive to it when___13___to it often enough.
The explanation for insensitivity to smell seems to be that the brain finds it___14___to keep all smell receptors working all the time but can___15___new receptors if necessary. This may___16___explain why we are not usually sensitive to our own smells -- we simply do not need to be. We are not___17___of the usual smell of our own house, but we___18___new smells when we visit someone else's. The brain finds it best to keep smell receptors___19___for unfamiliar and emergency signals___20___the smell of smoke, which might indicate the danger of fire.
1. [A] although [B] as [C] but [D] while
2. [A] above [B] unlike [C] excluding [D] besides
3. [A] limited [B] committed [C] dedicated [D] confined
4. [A] catching [B] ignoring [C] missing [D] tracking
5. [A] anyway [B] though [C] instead [D] therefore
6. [A] even if [B] if only [C] only if [D] as if
7. [A] distinguishing [B] discovering [C] determining [D] detecting
8. [A] diluted [B] dissolved [C] dispersed [D] diffused
9. [A] when [B] since [C] for [D] whereas
10. [A] unusual [B] particular [C] unique [D] typical
11. [A] signs [B] stimuli [C] messages [D] impulses
12. [A] at first [B] at all [C] at large [D] at times
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(编辑：rara)
