听课
课程与PC端同步更新，充分利用零碎时间。做题
海量精选试题，想练就练，瞬间提分。答疑
海量精选试题，想练就练，瞬间提分。直播
名师大咖面对面，有问有大收获多。1. 通读下面的短文，掌握其大意。然后每小题的四个选项中选出可填入相应空白处的最佳选项。
Enough sleep is important to health. The amount of sleep 21 depends on the age of the person and the conditions in which sleep 22 .The young may need more sleep than the old， but generally eight hours are enough for the health of grown-ups. Some can 23 with less than this amount but 24 may need more. Every person knows his own need. It is then a matter of how to 25 it. Sleep should always be enough to make one relaxed(松弛) and ready for 26 work.
Fresh air is 27 to sound sleep(酣睡). It is not without reason for some people to 28that it is practical to sleep in the open air. 29 a person can keep himself warm， out-of-door sleeping probably gives the body 30 complete relaxation.
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