用户数据报协议UDP属于TCP/IP参考模型的( )
A．应用层
B．传输层
C．互连层
D．主机-网络层
参考答案：B
________ your blog, I would have written back two days ago.
A．If I read
B．Should I read
C．Had I read
D．If I could have read
怎样正确使用“119”报警电话？
