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It seems to shine unchangingly, pouring out a constant light year after year. But the sun

may not be nearly so stable as we suppose. It is now thought to move quickly and irregularly and change in long-term cycles, growing dimmer and then brighter with each passing year. Some even fear that its frequent changing behavior. would have a great influence on the Earth' s climate.

The source of the sun' s inconstancy is magnetism. Professor William Livingston has developed new theories about its magnetic nature.

"We don' t yet know what causes sun spots, "he says, "but we now think they ' re areas of high level magnetism that come up from the sun' s interior. So strong is their magnetic pull that the highly ionized gas nearby is not able to transmit energy out. "As a result these areas send out less heat and light and thus appear from Earth to be almost dark irregular surface patches.

Sun spot activity generally fluctuates in steady, 11-year cycled. Scientists have long formed the o pinion that as the size and number of sun spots increased, the overall energy sent out by the sun would de crease. Indeed, recent studies confirmed it, revealing that during peak periods of sun spot activity, the Earth experiences a small drop that can be seen clearly in received solar energy.

Could such a small drop in energy have an effect here on earth？ Perhaps some scientists think the world temperature could fall by' as much as 0.2 during periods of high solar magnetism.., enough to cause significant fluctuations in weather patterns.

According to the passage, it is believed that the sun ______ ．

A．moves in a quick but steady way year after year

B．sends out less and less heat and light with each passing year

C．radiates the same amount of light every year

D．might have a strong influence on the weather patterns

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发布时间：2020-09-17

更多“It seems to shine unchangingly, pouring out a constant light year after year. But the sun”相关的问题

第1题

下面哪些是K-中心点算法？（)

A.PAM

B.CLARA

C.CLARANS

D.SHINE

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第2题

I did not switch on the light in case it should ________ her

A.glare

B.shine

C.faint

D.dazzle

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第3题

Well, no gain without pain, they say. But what about pain without gain？ Everywhere you go

in America, you hear tales of corporate revival. What is harder to establish is whether the productivity revolution that businessmen assume they are presiding over is for real.

The official statistics are mildly discouraging. They show that, if you lump manufacturing and services together, productivity has grown on average by 1.2% since 1987. That is somewhat faster than the average during the previous decade. And since 1991, productivity has increased by about 2% a year, which is more than twice the 1978 - 1987 average. The trouble is that part of the recent acceleration is due to the usual rebound that occurs at this point in a business cycle, and so is not conclusive evidence of a revival in the underlying trend. There is, as Robert Rubin, the treasury secretary, says, a "disjunction" between the mass of business anecdote that points to a leap in productivity and the picture reflected by the statistics.

Some of this can be easily explained. New ways of organizing the workplace--all that re-engineering and downsizing--are only one contribution to the overall productivity of an economy, which is driven by many other factors such as joint investment in equipment and machinery, new technology, and investment in education and training. Moreover, most of the changes that companies make are intended to keep them profitable, and this need not always mean increasing productivity: switching to new markets or improving quality can matter just as much.

Two other explanations are speculative. First, some of the business restructuring of recent years may have been unsuitably done. Second, even if it was well done, it may have spread much less widely than people suppose.

Leonard Schlesinger, a Harvard academic and former chief executive of Au Bon Pain, a rapidly growing chain of bakery cafes, says that much "re-engineering" has been crude. In many cases, he believes, the loss of revenue has been greater than the reductions in cost. His colleague, Michael Beer, says that far too many companies have applied re-engineering in a mechanistic fashion, chopping out costs without giving sufficient thought to long-term profitability. BBDO' s Al Rosen Shine is blunter. He dismisses a lot of the work of re-engineering consultants as mere rubbish—"the worst sort of ambulance-chasing."

It can be inferred form. the passage that the American economic situation is______.

A．not as good as it seems

B．at its turning point

C．encouraging

D．on the way to complete recovery

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第4题

There is nothing like the joy of finding out that something sinful is actually good for yo

u, whether it's sex, chocolate or a glass of fine zed wine—or, for that matter, beer, whisky or a satisfying aperitif. We've long heard exciting hints that red wine has unique benefits for the heart. But the same sunny reputation for heart health is now starting to shine on all liquor. "No matter where you look, the dominant alcoholic beverage is beneficial—whether it's red wine in France and Italy, sake in Japan or beer in Germany," says Dr. Walter Willett, chair of nutrition at the Harvard School of Public Health.

This has led researchers to an inescapable conclusion. As healthful as components of red wine may be, the primary benefit must come from ethanol itself. In short, it's the alcohol, stupid. But don't go overboard. Protection comes only with light to moderate intake—two drinks a day for men or a miserly one a day for women.

The major benefit of alcohol seems to come from its ability to boost levels of HDL, the good cholesterol that helps keep arteries clear of plaque. Ethanol does that by signaling the liver to make more of a substance called Apo Al, the major protein in HDL. The effects can be striking. "Depending on the individual, you can get increases of 10 to 30 percent in HDL in a week," says Harvard epidemiologist Eric Rimm. Alcohol also makes blood less sticky and less likely to form. clots that cause heart attacks and strokes. It also appears to have mild anti-inflammatory effects. And it enhances insulin sensitivity—which may explain why moderate alcohol consumption correlates with a lower incidence of type 2 diabetes.

But alcohol is a dietary Jekyll and Hyde. Heavy intake can raise blood pressure, increase irregular heartbeat, and lead to heart failure. The most sobering news concerns cancer. A recent analysis of 156 studies found that as alcohol intake increases, so do risks of tumors in the mouth, and liver. Even moderate drinking can boost breast-cancer risk a small amount.

Is moderate drinking worth the risks？ For some people—pregnant women, people with liver disease or a history of alcoholism—the answer is no. But for most of us, the benefits will probably outweigh the hazards. Whether you sip wine, beer or spirits, your heart may thank you.

According to Dr. Walter Willett, for good health, people could drink

A．only red-wine.

B．beer.

C．some whisky.

D．any alcohol.

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第5题

的一般项un=______；

的一般项u_n=______；

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第6题

的一般项un=______．

的一般项u_n=______．

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第7题

光伏发电站低电压穿越的最低电压要求为（)。

A.0%Un

B.5%Un

C.10%Un

D.20%Un

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第8题

（)若则∑n=1+∞|un|必发散．

( )若则∑_n=1^+∞|u_n|必发散．

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第9题

The manager of the customer service department seems ______ （replace).

The manager of the customer service department seems ______ (replace).

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第10题

证明：若，则∑n=1∞un发散．

证明：若，则∑_n=1^∞u_n发散．

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