BPCU控制左右系统在什么情况下连接（）。

A.GCB1断开

B.左或右转换汇流条无电

C.外接电源是唯一的电源

D.APU电源是唯一的电源

A “check” line is（）.

A.a safety line attached to a man working over the side

B.used to measure water depth

C.used to slow the headway of a barge

D.used to measure the overhead height of a bridge