如图所示，是一列简谐横波在某时刻的波形图.若此时质元P正处于加速运动过程中，则此时( )
A．质元Q和质元N均处于加速运动过程中
B．质元Q和质元N均处于减速运动过程中
C．质元Q处于加速运动过程中，质元N处于减速运动过程中
D．质元Q处于减速运动过程中，质元N处于加速运动过程中
答案：D
题目分析：因为质元P处于加速过程，所以质元P向平衡位置运动，由此可知波沿x轴负方向运动，所以质元Q沿y轴正方向运动，远离平衡位置，速度减小，质元N沿y轴正方向运动，靠 * * 衡位置，速度增大，故选项ABC错误D正确．
| 阅读下面短文，掌握其大意。然后从A、B、C、D四个选项中选出最佳选项。 | ||||
| Many scientists say that the world is getting hotter and hotter. If they are right, the ice at the North and South Pole will melt eventually. If this happens, the sea will rise and may cover most 1 all of Singapore. This will force everybody to move to a 2 country. We know that the sun 3 the earth. The heat from the sun hits the 4 , and some of it goes back into the sky. However, factories and cars 5 a lot of carbon dioxide (二氧化碳). When the gas rises into the sky, the heat from the sun can come 6 them but the heat from the ground cannot. It 7 near us in the sky and makes the 8 hotter and hotter every year. Scientists call this the "greenhouse effect" because a greenhouse is a small glass 9 which is hot inside. It is used for growing plants in cool countries. Many countries are 10 about the greenhouse effect. They are trying to stop factories and cars from sending 11 gases into the sky. Scientists are not sure when the world will get much hotter. Some people say that the greenhouse effect has 12 already and has begun to affect the world's weather. | ||||
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