题目

电量为q的点电荷，在两个固定的等量异种电荷＋Q和－Q的连线的垂直平分线上移动，则(    ) A．电场力做正功                        B．电场力做负功 C．电场力不做功                        D．电场力做功的正负，取决于q的正负 答案：C16．（1）He had to go to the library．（改为一般疑问句）Did he have togo to the library？（2）I want you to go to your room at once．（改为否定形式）I don't want you to go to your room at once．（3）The handbag is very lovely，isn't it？（写出反义疑问句）（4）I have had to stay there for a week．（就划线部分提问）How long have you had to stay there？（5）He says，"I come from Australia．"（改为间接引语）He says that he comes from Australia．．