单项选择题

A.CHAP=2,表示Immediate Assignment on TCH, SDCCH Chosen First 
B.如果CHAP=2,则在立即支配过程中永远不会占用SDCCH
C.如何为短消息业务,不管CHAP设为1还是2,均不会立即指配到TCH上 
D.CHAP=3,表示Immediate Assignment on TCH, TCH Chosen First, GSM Phase 2 Mobiles, "Channel Needed" Supported