问答题简答题：单相变压器的一次电压U1＝3000V，变比K＝15，求二次电压U2；当一次电流I1＝

题型：问答题简答题

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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 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 changeour 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 ha1f-hour snooze (瞌睡) every afternoon.

About 60 percent of American adults nap when given the opportunity. We seem to have"a

mid afternoon 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.

l. It is commonly accepted in American society that too much sleep is ._____

A. unreasonable

B. criminal

C. harmful

D. costly

2. 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 traffic accidents

3. 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

4. The underlined phrase "American sleep debt" in 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

5. 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

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单相变压器的一次电压U1＝3000V，变比K＝15，求二次电压U2；当一次电流I1＝

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