题目内容：
Enough sleep is important to health. The amount of sleep21depends on the age of the per-son and the conditions in which sleep22. The young may need more sleep than the old, but 23eight hours are enough for the health of grown-ups. Some can do with less than this amountbut24may need more. Every person knows his own need. It is then a matter of how to25 it. Sleep should be always enough to make one relaxed (松弛)and ready for26work. Fresh air is27to sound sleep(酣睡). It is not28reason for some people to insist thatit is practical to sleep in the open air.29a person can keep himself warm,out-of-door sleepingprobably gives the body30complete relaxation.
Ability to sleep is largely a habit. The conditions referred to only lead to sleep. Out-of-door 31, a good habit of regular drinking and the avoidance of late eating and32are all helpfulto sound sleep. Such factors are largely within the33of any person. A bath at34, neitherhot nor cold but of body temperature, may be helpful to sleep. Sleeping pills should never be takenexcept when suggested by35.
根据以上内容,回答题.
第21答案是（ ） A．wished
B．expected
C．Needed
D．wanted
参考答案：
答案解析：