．如图所示，竖直绝缘墙壁上的Q处有一固定的质点A，在Q的正上方的P点用丝线悬挂另一质点B， A、B两质点因为带电而相互排斥，致使悬线与竖直方向成
角，由于缓慢漏电使A、B两质点的带电量逐渐减小。在电荷漏完之前悬线对悬点P的拉力大小（ ）
A.保持不变 B.先变大后变小 C.逐渐减小 D.逐渐增大
答案：A
对带电小球受力分析，利用力三角形与几何三角形相似列出比例式子，既可得出答案为A。
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| I used to live selfishly, I should admit. But one moment changed me. I was on my lunch break and had 1 the office to get something to eat. On the way, I 2 a Busker (街头 艺人), with a hat in front of him. I had some 3 in my pocket, but I would not give them to him, thinking to myself he would 4 use the money to feed his addiction to drugs or alcohol. He 5 like that type-young and ragged. 6 what was I going to spend the money on? Only to feed my addiction to Coca-Cola or chocolate! I then 7 I had no right to place myself above 8 just because he was busking. I 9 and dropped all the coins into his 10 , and he smiled at me, I watched for a while. As 11 as it sounds, I expected something more to come from that moment-a feeling of 12 or satisfaction, for example. But nothing happened 13 , I walked off. "It proved to be a waste of 14 ," I thought. On my way home at the end of the 15 , I saw the busker again and he was 16 . I watched him pick up the hat and walk 17 a cafe counter. There he poured the 18 contents into a tin collecting 19 an earthquake fund- raising (募捐) event. He was busking for charity (慈善)! Now I donate any 20 I have to charity tins and enjoy the feeling of giving. | ||||
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