1. [单选题]What is the purpose of the spanning-tree algorithm in a switched LAN?
A. To provide a monitoring mechanism for networks in switched environments.
B. To manage VLANs across multiple switches.
C. To prevent switching loops in networks with redundant switched paths.
D. To segment a network into multiple collision domains.
E. To prevent routing loops in networks.
2. [单选题]在启用IGRP协议时，所需要的参数是：()
A. 网络掩码
B. 子网号
C. 自治系统号
D. 跳数
3. [单选题]配置路由器时，封装PPP协议的命令是：()
A. encap ppp
B. ppp
C. group ppp
D. int ppp
