单项选择题
A. Serial 0 is up, line protocol is up
B. Serial 0 is up, line protocol is down
C. Serial 0 is down, line protocol is down
D. Serial 0 is down, line protocol is up
E. Serial 0 is administratively down, line protocol is down
F. Serial 0 is administratively down, line protocol is up
单项选择题 There is a connectivity problem between the serial 0/0 interface of router TESTKING1 and the serial 0/0 interface of TESTKING2. A leased line point to point circuit is installed between these two routers. The output from the "show interface serial 0/0" command is displayed below for each of these routers: From your observations of the above exhibit, what is the underlying cause of the problem?（）
单项选择题 The relevant configuration files for the TestKing1 and TestKing2 routers are displayed below: With due consideration to the command outputs, which of the following reasons would you attribute the connectivity problem between the two routers?（）
单项选择题 What kind of message does a PING send out to test connectivity?（）