The SOURCE OFF light will illuminate:
A.A.When the source selected to power the transfer bus has failed and the automatic bus transfer function has closed the BTBs to power the transfer bus from another source
B.B.When the source selected to power the Transfer bus and the automatic transfer function have both failed resulting in the transfer bus being. Unpowered
C.C.When the TRANSFER BUS OFF light is illuminated
D.D.All of the above
正确答案是D