以下哪个信令协议属于共路信令（）。

A.Busy High Call Ability
B.Busy High Call Attempt
C.Busy Hour Call Ability
D.Busy Hour Call Attempt

A.DTU
B.MRS
C.MRU
D.SMCU

A.480+480
B.320+320
C.240+240
D.120+120