题目

如图所示，质量为m的铁球从空中位置A处由静止释放后，经过一段时间下落至位置B，A、B间高度差为H，重力加速度为g，不计空气阻力，取A位置为零势能点。则（ ）A. 在位置B处，铁球的重力势能为 mgHB. 如果存在空气阻力，在位置B处铁球的重力势能大于C. 无论是否存在空气阻力，经过位置B处时，重力势能一定减小mgHD. 选择B为零势能点，由于零势能点下降，重力做功会大于mgH阅读理解。      An expensive car speeding down the main street of a small town was soon over-taken by a young motorcycle policeman. As he started to take out the ticket, the woman in the car said proudly. "Before you go any further, young man, I think you should know that the mayor of this city is a good friend of mine. "     The officer did not say a word, but kept writing.     "I am also a friend of Chief of Police Barnes,"continued the woman, getting angrier each moment.     Still he kept on writing.     "Young man," she said, "I know Judge Lawson and State Senator Patton. "     Handing the ticket to the woman,the officer asked pleasantly. "Tell me, do you know Bill Bronson?"     "No. Why?" she replied.     " Well, this is the man you should have known," he said, going back to his motorcycle,"I am Bill Bronson. "1.The policeman stopped the car because  ___  .A. it was an expensive carB. the driver was a proud ladyC. the driver was driving too fastD. the driver was going to attack him2. The woman was getting angrier each moment because  __   .A. the policeman didn't know her friendsB. the policeman kept writing the ticket for herC. the policeman refused to accept her offer of moneyD. she didn't know the policeman's name3. The woman driving the expensive car  __   .A. failed to stop the policeman writing the ticketB. warned the policeman not to move a step furtherC. was surprised that the policeman did not know the mayorD. told the policeman to stay where he was4. The policeman was   __  .A. an honest and fair fellowB. a foolish and proud fellowC. a silly and rude fellowD. a kind-hearted fellow5. The policeman   __  . A. had no sense of humorB. had a sense of humorC. had no sense of dutyD. was playing a joke on the woman