1. [多选题]CDP is being used throughout the Ezonexam network. What are two reasons why the Ezonexam network administrator would use CDP? (Choose two)
A. To determine the status of network services on a remote device
B. To obtain the IP Address of a connected device in order to telnet to the device
C. To verify the type of cable interconnecting two devices
D. To verify Layer 2 connectivity between two devices when Layer 3 fails
E. To obtain VLAN information from directly connected swticehs
F. F. To determine the status of the routing protocols between directly connected routers
G. G. To support automatic network failover during outages
2. [单选题]OSI第二层数据封装完成后的名称是：()
A. 比特
B. 包
C. 帧
D. 段
3. [单选题]关于PPP和HDLC的说法中，错误的是（）
A. PPP是通用协议，HDLC是CISCO私有协议
B. PPP有验证功能，HDLC无验证功能
C. PPP效率低，HDLC效率高
D. 在配置ISDN时，广域网协议不能封装成PPP，但可以封装成HDLC
