题干
I am sorry to have kept you for a long time.
A：wait
B：to wait
C：waiting
D：waited
答案(点此获取答案解析）
C
I am sorry to have kept you for a long time.
A：wait
B：to wait
C：waiting
D：waited
入一交流电源，副线圈电路中R1、R2、R3和R4均为定值电阻，开关S是闭合的．V1和V2为理想电压表，读数分别为U1和U2；A1、A2和A3为理想电流表，读数分别为I1、I2和I3．现断开S，U1数值不变，则下列推断中正确的是