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问题 单项选择题

虚拟存储管理系统的基础是程序的 (6) 理论，这个理论的基本含义是指程序执行时往往会不均匀地访问主存储器单元。根据这个理论，Denning提出了工作集理论。工作集是进程运行时被频繁访问的页面集合。在进程运行时，如果它的工作集页面都在 (7) 内，则能够使该进程有效地运行，否则会出现频繁的页面调入/调出的现象。

A．全局性

B．局部性

C．时间全局性

D．空间全局性

答案

参考答案：B

单项选择题

For many years, people () electric cars. However, making them has been more difficult that predicted.

A. had dreamed of

B. have dreamed of

C. dreamed of

D. dream of
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问答题

If a heavy reliance on fossil fuels makes a country a climate ogre, then Denmark — with its thousands of wind turbines sprinkled on the coastlines and at sea — is living a happy fairy tale.
Viewed from the United States or Asia, Denmark is an environmental role model. The country is "what a global warming solution looks like," wrote Frances Beinecke, the president of the Natural Resources Defense Council, in a letter to the group last autumn. About one-fifth of the country’s electricity comes from wind, which wind experts say is the highest proportion of any country.
But a closer look shows that Denmark is a far cry from a clean-energy paradise. The building of wind turbines has virtually ground to a halt since subsidies were cut back. Meanwhile, compared with others in the European Union, Danes remain above-average emitters of the greenhouse gas carbon dioxide. For all its wind turbines, a large proportion of the rest of Denmark’s power is generated by plants that burn imported coal.
The Danish experience shows how difficult it can be for countries grown rich on fossil fuels to switch to renewable energy sources like wind power. Among the hurdles are fluctuating political priorities, the high cost of putting new turbines offshore, concern about public acceptance of large wind turbines and the volatility of the wind itself.
"Europe has really led the way," said Alex Klein, a senior analyst with Emerging Energy Research, a consulting firm with offices in Cambridge, Massachusetts.
Some parts of western Denmark derive 100 percent of their peak needs from wind if the breeze is up. Germany and Spain generate more power in absolute terms, but in those countries wind still accounts for a far smaller proportion of the electricity generated. The average for all 27 European Union countries is 3 percent.
But the Germans and the Spanish are catching up as Denmark slows down. Of the thousands of megawatts of wind power added last year around the world, only 8 megawatts were installed in Denmark.
If higher subsidies had been maintained, he said, Denmark could now be generating close to one-third — rather than one-fifth — of its electricity from windmills.
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