单项选择题

A.语音业务:BTS-GEIUB-GTNU-GEIUT-GEIUT-GTNU-GDPUC=GTNU-GEIUA-MSC
B.接口7号信令:MSC-GEIUA-GSCU-GEIUT-GEIUT-GSCU-GXPUM
C.分组业务:BTS-GEIUB-GTNU-GEIUP-PCU
D.Abis接口信令:BTS-GEIUB-GSCU-GXPUM