【单选题】An external power source can be connected to the AC tie bus through the external power receptacle and the external power contactor( EPC ). choose the rihgt answer:
A.
the external power source is AC electrical power
B.
the external power receptacle is in the cockpit
C.
the external power contactor is on the overhead panel in the cockpit
D.
the AC tie bus is used carry passengers and is driven by AC power