【单选题】An administrator issues the show ip interface s0/0 command and the output displays that interface Serial0/0 is up, line protocol is up. What does 'line protocol is up' specifically indicate about the ...
A.
The cable is attached properly.
B.
CDP has discovered the connected device.
C.
Keepalives are being received on the interface.
D.
A carrier detect signal has been received from the connected device.