VPN服务器所使用的WAN微型端口有（）。
A.PPP
B.PPTP
C.L2TP
D.TCP
参考答案：B, C
The Diaoyu Islands _____ in Chinese maps since the 14th and 15th centuries.
A．have been included
B．had been included
C．were included
D．are included
书面形式的要约自( )时发生效力。
A．到达受要约人 B．要约人发出C．受要约人了解要约内容 D．受要约人作出承诺
