一Hey! There is a bag on the ground. Whose is it?

一There is a woman over there. Maybe it's ______.[ ]

A. her

B. hers

C. she

D. herself

电力系统发生振荡时，各点电压和电流（）。

A.均作往复性摆动；

B.均会发生突变；

C.在振荡的频率高时会发生突变；

D.不变。