单项选择题 Which command generates a BERT test pattern of alternating ones and zeros on T1 number 1 for one minute?（）

单项选择题 Which command displays the results of a loopback test you executed on a CT3 line module in slot 5, port 0, t1 number 4?（）

单项选择题 Which command is used on the local router to invoke a loopback mode on a remote ERX Edge Router?（）