Telnet服务使用的默认端口号是（）。
A.80
B.23
C.8080
D.21
参考答案：B
---The man in a black suit _______ be our youth worker.
---It _______ be him. I saw him in the classroom building some minutes ago.
A．can; could
B．must; can’t
C．can; mustn’t
D．must; won’t
冷却作用
