题目

 Not until the motorbike looked almost new        repairing and cleaning it.   A. he stopped                                 B. did he stop        C. stopped he                                 D. he did stop 答案：B两圆环A.B置于同一水平面上，其中A为均匀带电绝缘环，B为导体环，当A以如图所示的方向绕环心转动的角速度发生变化时，B中产生如图所示方向的感应电流，则（ ）A.A可能带正电且转速增大 B.A可能带正电且转速减小C.A可能带负电且转速减小 D.A可能带负电且转速增大