多项选择题
A. limited error checking
B. defined timers
C. no recovery mechanisms
D. three-way handshake
单项选择题 Which command will delete the current rescue configuration?（）
单项选择题 Using the routing table shown in the exhibit, what will be the next-hop IP address used for destination IP address 192.168.1.1? （）
单项选择题 You have been asked to use a 23-bit network mask to segment the network block 209.18.12.0, How many usable host address will there e per subnet?（）