问题:
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 u
● 参考解析
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