在如图所示的电路中，电源电压保持不变。闭合开关S后，向右移动滑片P。下列说法中正确的是（ ）
A．电压表的示数变大
B．电压表的示数变小
C．电流表A的示数变大
D．电流表
的示数变小
答案：D
题目分析：由图可知，两电阻并联，电压表测电源的电压，电流表A1测干路的电流，电流表A测滑动变阻器R1的电流。闭合开关S后，向右移动滑片P，滑动变阻器R1的阻值增大，通过滑动变阻器R1的电流变小，干路的电流变小，即电流表A的示数变小，电流表A1的示数变小，电压表的示数不变。故选D
| 完形填空。 | ||||
| Being alone in outer space can be frightening. That is one reason why astronauts on solo (单独的) space flights are given plenty of work to keep them 1 . There are also constant communications with people on the earth. 2 , being with people from whom you cannot get away might be even harder than being 3 . This is what happens on long submarine (潜水艇) voyages. It will also happen on 4 space flights in the future. Will there be special problem of adjustment (调整) under such 5 ? Scientists have studied the reactions (反应) of men to one another during long submarine 6 . They have found that the longer the voyage 7 , the more serious the problem of 8 is. When men are 9 together for a long period, they begin to feel uneasy. Everyone has little habits of speaking and behaving that are ordinarily acceptable. In the limited space over a long period of time, however, these little habits may become very 10 . Although no one wants to be 11 all the time, everyone needs some degree of privacy(隐私). When people are enclosed together, they are in what is called a stress situation. That means that they are under an unusual amount of 12 or stress. People who are well-adjusted are able to 13 stress situations better than others. That is one reason why so much 14 is taken in choosing our astronauts. These men undergo (经历) a long period of 15 and training. One of the things tested is their behavior under stress. | ||||
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不能稳定存在。