1. [单选题]OSI七层模型中，“包”是哪一层数据封装的名称（）
A. 物理层
B. 数据链路层(data link layer)
C. 网络层
D. 传输层
2. [单选题]A Ezonexam technician is troubleshooting connectivity problems between two routers that are directly connected through the serial line. The technician notices that the serial line is up but cannot see any neighbors displayed in the output of the show cdp neighbors command.In which OSI layer is the problem most likely occurring?
A. Physical
B. Data link
C. Network layer
D. Transport layer
E. Application layer
3. [多选题]网络中经常使用“帧中继”服务，请选出帧中继的优点（）
A. 偷占带宽
B. 提供拥塞管理机制
C. 可以使用任意广域网协议
D. 灵活的接入方式
4. [单选题]OSI七层模型中，“段”是哪一层数据封装的名称（）
A. 物理层
B. 数据链路层(data link layer)
C. 网络层
D. 传输层
5. [单选题]A Ezonexam PC has the IP address 172.16.209.10 /22. What is the subnet of this address?
A. 172.16.42.0
B. 172.16.107.0
C. 172.16.208.0
D. 172.16.252.0
E. 172.16.254.0
