1. [单选题]The Ezonexam network administrator has issued the "VTP password ezonexam" command on a Cisco device. What is the purpose of this command?
A. It allows two VTP servers to exists in the same domain, each configured with different passwords
B. It is the password required when promoting a switch from VTP client mode to VTP server mode
C. It is used to access the VTP server to make changes to the VTP configuration
D. It is used to validate the sources of VTP advertisements sent between switches
E. None of the above
2. [多选题]网络中经常使用DDN服务，请选出DDN的优点（）
A. 传输质量高
B. 接入方式灵活
C. 偷占带宽
D. 使用虚电路
E. 专用线路
3. [单选题]路由器上的命令“show version”的功能是（）
A. 显示版本信息
B. 显示端口配置信息
C. 显示路由表
D. 显示路由协议信息
