—Where does he come from?

—I know nothing about him except that he is a doctor      occupation.

A．in

B．by

C．through

D．for

高压断路器能根据需要，将电路设备或线路投入（或退出）运行，能在某些电气设备或线路发生故障时，将（）从电网中快速切除，保证电网无（）正常运行。