信号消息路由选择属于NO.7信令网功能级中第几级功能。（）
A、1
B、2
C、3
D、4
参考答案：C
It must have rained last night, ______? [ ]
A. mustn't it
B. can't it
C. hasn't it
D. didn't it
借代分类有哪些？
