回避制度
参考答案：
— Why didn't you come and open the door for me, dear?
— Oh, sorry, I _____ in the kitchen. I didn't hear you. [ ]
A. cooked
B. would cook
C. was cooking
A．，正电荷
B．，正电荷
C．，负电荷
D．，负电荷
，正电荷
，正电荷
，负电荷
，负电荷