单项选择题 Which of the following is used to serve as an emergency backup line to troubleshoot a broadbandconnection on many routers?（）

单项选择题 An administrator wants to test the network MTU. Which of the following commands allows differentsize packets to be sent?（）

单项选择题 An administrator suspects that an incorrect POTS line is carrying the DSL signal. Which of thefollowing will help diagnose this issue?（）