题目

如图10所示，要使两灯串联，应闭合开关       ，闭合开关S1和S3，两灯     联;为了避免短路,不能同时闭合开关        。  答案：S2_____  ____并联_____   ___S2S3_解析:略He is ________ the suona but then the doorbell rings. ( )A. playing B. plays C. played