Tom and Mike are good friends. They often         each other from being punished by the          teacher.

A．prevent

B．settle

C．shelter

D．prefer

（）是指变配电所中承担输送和分配电能任务的电路，其中的设备成为一次设备。

A.控制回路

B.保护回路

C.一次回路

D.二次回路