将电气设备的金属外壳与变压器的零线连接在一起，以保护人身的安全叫（）
A.工作接地
B.保护接地
C.保护接零
D.重复接地
参考答案：C
培养儿童自制力的关键期在（）
A.1岁
B.2岁
C.3岁
D.4岁
E.5岁
33. Only when ____in the afternoon _____able to leave.
A．the match was over; they were
B．was the match over; were they
C．was the match over; they were
D．the match was over; were they
