Questions 21 to 25 are based on the following passage
American society is not nap (睡) friendly. In fact, says David Dinges, a sleep specialist at the University of Pennsylvania School of Medicine. "There's even a prohibition against admitting we need sleep". Nobody wants to be caught napping or found asleep at work. To quote a proverb: "Some sleep five hours, nature requires seven, laziness nine and wickedness eleven. "
Wrong. The way not to fall asleep at work is to take naps when you need them. "
We have to totally change our attitude toward napping", says Dr. William Dement of Stanford Univereity, the godfather of sleep research.
Last year a national commission led by Dement identified an "American sleep debt" which one member said was as important as the national debt, The commission was concerned about the dangers of sleepiness: people causing industrial accidents or falling asleep while driving. This may be why we have a new sleep policy in the White House. According to recent reports, president Clinton is trying to take a halfhour snooze (睡) every afternoon.
About 60 percent of American adults nap when given the opportunity. We seem to have "a midafternoon quiet phase"also called"a secondary sleep gate. "Sleeping 15 minutes to two hours in the early afternoon can reduce stress and make us refreshed. Clearly, we were born to nap.
We Superstars of Snooze don't nap to replace lost shuteye or to prepare for a
night shift. Rather, we"snack"on sleep, whenever, wherever and at whatever time we feel like it. I myself have napped in buses, cars, planes and on boats; on floors and beds; and in libraries, offices and museums.

21. It is commonly accepted in American society that too much sleep is ______ .
A) unreasonable
B) criminal
C) harniful
D) costly

22. The research done by the Dement commission shows that Americans ______ .
A) don't like to take naps
B) are terribly worried about their national debt
C) sleep less than is good for them
D) have caused many industrial and traftic accidents

23. The purpose of this article is to ______ .
A) warn us of the wickedness of napping
B) explain the danger of sleepiness
C) discuss the side effects of napping
D) convince the reader of the necessity of napping

24. The "American sleep debt"( Line 1, Para. 3) is the result of ______ .
A) the traditional misconception the Americans have about sleep
B) the new sleep policy of the Clinton Administration
C) the rapid development of American industry
D) the Americans' worry about the danger of sleepiness

25. The second sentence of the last paragraph tells us that it is ______ .
A) preferable to have a sound sleep before a night shift
B) good practice to eat something light before we go to bed
C) essential to make up for cost sleep
D) natural to take a nap whenever we feel the need for it