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问题 选择题

关于太阳辐射的叙述正确的是（　　）

A．太阳是以电磁波的形式源源不断地向四周放射能量的

B．太阳辐射的能量来源于太阳内部的氢原子核的核裂变反应，即氢核在分裂的过程中，释放能量

C．太阳辐射能在地面的分布是不均匀的，因而对于整个地球表层来说，热量是不平衡的

D．太阳辐射每分钟释放相当于燃烧4亿吨烟煤的热量，但这并不对太阳的质量造成任何影响

答案

答案：A

太阳辐射能量来源于氢核的核聚变反应，在核聚变过程中，损失的质量转变为能量释放(核电厂是通过铀原子的裂变产生能量的)；太阳辐射的能量在地面分布是不均匀的，但地球表层的能量的输入和支出却是平衡的，不然地球表面的温度将持续升高或降低。

单项选择题

There is no question that the academic enterprise has become increasingly global, particularly in the sciences. Nearly three million students now study outside their home countriesa 57% increase in the last decade. Foreign students now dominate many U.S. doctoral programs, accounting for 64% of Ph. D. s in computer science, for example.
Faculty members are on the move, too. Half of the world’s top physicists no longer work in their native countries. And major institutions such as New York University are creating branch campuses in the Middle East and Asia. There are now 162 satellite campuses worldwide, an increase of 43% in just the past three years.
At the same time, growing numbers of traditional source countries for students from South Korea to Saudi Arabia (沙特阿拉伯), are trying to improve both the quantity and quality of their own degrees, engaging in a fierceand expensiverace to recruit students and create world-class research universities of their own.
Such competition has led to considerable hand-wringing in the West. During a 2008 campaign stop, for instance, then—candidate Barack Obama expressed alarm about the threat that such academic competition poses to U. S. competitiveness. Such concerns are not limited to the United States. In some countries, worries about educational competition and brain drains have led to academic protectionism. India, for instance, places legal and bureaucratic barriers in front of Western universities that want to set up satellite campuses to enroll local students.
Perhaps some of the anxiety over the new global academic enterprise is understandable, particularly in a period of massive economic uncertainty. But educational protectionism is as big a mistake as trade protectionism is. The globalization of higher education should be embraced, not fearedincluding in the United States. There is every reason to believe that the worldwide competition for human talent, the race to produce innovative research, the push to extend university campuses to multiple countries, and the rush to train talented graduates who can strengthen increasingly knowledge-based economies will be good for the United States, as well.

In the last paragraph, the author tries to emphasize that ______.

A. the academic enterprise has become global
B. academic competition has led to protectionism
C. worries over educational competition are understandable
D. educational protectionism cannot be justified
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单项选择题

弹性滑动是由( )引起的，弹性滑动是( )避免的。

A．拉力差，可以

B．拉力差，无法

C．摩擦力，可以

D．摩擦力，无法
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