题目

如图所示的理想变压器，对于原、副线圈，一定相等的物理量是：A．交流电的最大值           B．磁通量的变化率 C．电功率                     D．交变电流频率 答案：BCDIn America, if__________friend has invited you to drop by anytime, it is__________best to call before visiting to make sure it is convenient for him.A．a; aB．a; 不填C．the; aD．the; 不填