题目

 ---Why! I couldn’t get you on the phone this morning.   ---We ____tennis in the yard when you phoned me.     A. could be playing  B. must be playing  C. must have been playing  D. should have played 答案： C如图所示，为小刚所连的两盏白炽灯和两上插座的电路图，通电后发现不能正常工作．下面几个措施中可能引起危险的是（ ）A．拆掉灯丙，两条导线连在一起B．拆掉插座甲，两条导线连一起C．拆掉开关S3，两条导线连在一起D．拆掉开关S2，两条导线连在一起