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问题 填空题

夏天清晨，树叶上常有一些露珠，透过露珠看叶脉，叶脉变________了，露珠相当于_________镜，叶脉的像是________像。（选填“虚”或“实”）

答案

大；凸透；虚

完形填空

How much sleep do we need? People are all different. Some people need only three or four hours of sleep a night. Others need ten hours of sleep a night. Most Americans sleep seven to eight hours a night.

Some people find it hard to fall asleep. About one in three(三分之一) Americans have a problem with sleep. Many of these people can not fall asleep. The name of this problem is insomnia(失眠症). Many famous people in history had insomnia. Some of these people have special(特殊的) ideas to make themselves sleep. Benjamin Franklin had four beds. He moved from bed to bed to fall asleep. Mark Twain lay(躺) on his side across the end of his bed.

根据短文内容，判断正(A)误(B)。（5分）

小题1:Different people need different amounts of sleep(睡眠时间).

小题2:Most Americans sleep more than 8 hours a night.

小题3:If a person has insomnia, he can never fall asleep.

小题4:About 1/3 of Americans have a problem with sleep.

小题5:Mark Twain had four beds to make himself sleep.
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单项选择题

（）是由于固体介质内热不稳定过程造成的击穿。

A.电击穿

B.热击穿

C.工频击穿

D.电化学击穿
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