The amount of sleep a human being needs depends on【C1】______ , the individua

游客2025-03-20 9

问题 The amount of sleep a human being needs depends on【C1】______ , the individual and possibly race. For example, doctors think that pre-school children need between 10 and 12 hours a night; school children between 9 and 11 hours; and adults between 7 and 9 hours. There are exceptional【C2】______ of old people who only sleep between 2 and 3 hours a day and continue to be active and healthy. The sleep requirements of different【C3】______ also appear to be different. Japanese people, for example, sleep fewer hours than Europeans.
It is not known for【C4】______ if mental activity(apart from dreaming)occurs when a person is asleep.【C5】______ , it is certainly true that some people can wake up at a specific, predetermined time. There are also【C6】______ about mathematicians who solve difficult problems during sleep, because their【C7】______ minds continue working on the problem.
Some types of unpleasant dreams(or "nightmares")are quite【C8】______ ; the dreamer is taking a test, but is not properly prepared; he is falling from a tree;【C9】______ an animal or thing is chasing him. Some people say these last two occur【C10】______ man’s ancestors lived in trees and were in constant danger from wild animals. [br] 【C5】

选项 A、Besides
B、Therefore
C、Hence
D、However

答案 D

解析上句提到，人在睡眠时除了做梦外是否会有智力活动产生还不能肯定地知道。下句说，有一点可以肯定的是，有些人能在某一具体、特定的时间里醒来。很明显，下句对上句而言，语气有所转折，因而正确答案应选D项However(但是，然而)。A项Besides(而且)、B项Therefore(因此)和C项Hence(所以)都不符合上下文的意思。

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