电气设备的外壳与接地的零线连接称为()。
参考答案:保护接零
There was a knock at the door. It was the second time someone _______ me that evening.
A.had interrupted
B.would have interrupted
C.to have intrrupted
D.to intrrupt
春运期限为()天。
A.40
B.50
C.60
D.70