1. [单选题]On a half-duplex Ethernet LAN, two hosts attempt to send data simultaneously, resulting in a collision. Following this collision, what will the hosts do? (Select all valid answers)
A. The destination host sends a request to the source for retransmission.
B. The jam signal indicates that the collision has been cleared.
C. The hosts will attempt to resume transmission after a time delay has expired.
D. An electrical pulse indicates that the collision has cleared.
E. The router on the segment will signal that the collision has cleared.
F. F. The hosts will do nothing, as the higher layers are responsible for data error correction and re-transmission.
2. [单选题]EIGRP的管理距离（）
A. 90
B. 100
C. 110
D. 120
3. [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
