大地回线转金属回线时用来断开大地回线中直流电流的开关为（）。

A.BPI

B.GTRS

C.MRTB

D.BPS

California seems to be the home of the homeless since many are often observed tramping along railroad tracks and through the downtown areas of the cities.

A．roaming

B．trimming

C．stealing

D．stamping