单项选择题
A. 15 seconds
B. 30 seconds
C. 180 seconds
D. 240 seconds
单项选择题 An administrator issues the command ping 127.0.0.1 from the command line prompt on a PC. If a reply is received, what does this confirm?（）
单项选择题 How does using the service password encryption command on a router provide additional security? （）
单项选择题 What is the maximum data rate specified for IEEE 802.11b WLANs?（）