Passage Three:Questions 21 to 25 are based on the following passage.American society is not nap (午睡) 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 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 University, 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 half-hour snooze (打瞌睡) 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 shut-eye 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. 第21题：It is commonly accepted in American society that too much sleep is ________. A) unreasonable B) criminal C) harmful D) costly