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（18分）

    一长木板在水平地面上运动，在t=0时刻将一相对于地面精致的物块轻放到木板上，以后木板运动的速度－时间图像如图所示。己知物块与木板的质量相等，物块与木板间及木板与地面间均有靡攘.物块与木板间的最大静摩擦力等于滑动摩擦力，且物块始终在木板上。取重力加速度的大小g＝10m／s2求:

        

物块与木板间；木板与地面间的动摩擦因数:

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单项选择题

一、根据以下资料，回答：2010年11月份，全国餐饮业实现零售额823.1亿元，比2004年同期增长14.5%，占社会消费品零售总额的13.9%，其增幅高出社会消费品零售总额4个百分点。预计2011年全年餐饮业零售额将达到8800亿元，2011年将突破万亿元大关。从2006年起，我国餐饮业零售额连续4年实现每年一个千亿元台阶的跨越，由2006年的4000亿元已增加到2009年的7486亿元，餐饮网点已达400多万个，零售额和网点数分别为1978年的136倍和34倍。2009年我国餐饮业零售额相当于全国GDP的5.84%、第三产业增加值的17.62%。我国餐饮业已连续14年保持两位数增长，增长幅度不仅高于我国GDP的增长速度，而且也高于我国社会消费品零售总额的增长速度，一直领先于消费品市场中的各个行业。餐饮业还成为我国吸纳就业的重要渠道。2009年我国餐饮业从业人员与1978年104.4万人相比，增长了16倍。

2010年11月我国社会消费品零售总额是（）。

A．937.5亿元

B．942.4亿元

C．5676.6亿元

D．5921.6亿元
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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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