1. [单选题]通配符掩码和子网掩码之间的关系是（）。
A. 两者没有什么区别
B. 通配符掩码和子网掩码恰好相反
C. 一个是十进制的，另一个是十六进制(hexadecimal system)的
D. 两者都是自动生成的
2. [单选题]配置路由器特权用户“加密密码”的命令是：()
A. password
B. enable password
C. enable secret
D. passwd
3. [单选题]You have a class C network, and you need to design it for 5 usable subnets with each subnet handling a minimum of 18 hosts each. Which of the following network masks should you use?
A. 225.225.224.0.
B. 225.225.240.0.
C. 225.225.255.0.
D. 255.255.255.224
E. 225.225.255.240
