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问题 选择题

一天中，陆地最高气温一般出现在（　　）

A．午前10时左右

B．午后2时左右

C．中午12时

D．午后4时左右

答案

一天中，最高气温一般出现在下午两点钟，最低气温一般出现在后半夜两点以后．

故选：B．

单项选择题

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.

55().

A.when 

B.since 

C.for 

D.whereas
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填空题

水体本身也有去除某些（）物质的能力。
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