从逻辑实体分类，SIP共包含三大逻辑实体（）。
A.UE
B.UA
C.PROXY
D.SERVER
参考答案：B, C, D
--- Thanks for your dinner .
--- _______________. [ ]
A. You eat well .
B. You are welcome.
C. Sorry , it isn't good .
D. Let's go home .
坚持正确舆论导向有何重要意义？
