问答题

(1) effect of the country’’s growing human population on its wildlife 　　(2) possible reason for the effect 　　(3) your suggestion for wildlife protection

【参考答案】

The two graphs here indicate the relation between the popula......

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The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, ________ this is largely because, ________ animals, we stand upright. This means that our noses are ________ to perceiving those smells which float through the air, ________ the majority of smells which stick to surfaces. In fact, ________ , we are extremely sensitive to smells, ________ we do not generally realize it. Our noses are capable of ________ human smells even when these are________to far below one part in one million.Strangely, some people find that they can smell one type of flower but not another, ________ others are sensitive to the smells of both flowers. This may be because some people do not have the genes necessary to generate ________ smell receptors in the nose. These receptors are the cells which sense smells and send ________ to the brain. However, it has been found that even people insensitive to a certain smell ________ can suddenly become sensitive to it when ________ to it often enough.The explanation for insensitivity to smell seems to be that the brain finds it ________ to keep all smell receptors working all the time but can ________ new receptors if necessary. This may ________ explain why we are not usually sensitive to our own smells―we simply do not need to be. We are not ________ of the usual smell of our own house, but we ________ new smells when we visit someone else’’ s. The brain finds it best to keep smell receptors ________ for unfamiliar and emergency signals ________ the smell of smoke, which might indicate the danger of fire.

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