The show controllers serial 0 command will show you whether either a DTE or DCE cable is connected to the interface. If it is a DCE connection, you need to add clocking with the clock rate command.
To completely replace the running-config with the startup-config, you must reload the router. Note : You may have picked option C, which isn't a bad answer. Remember, though, it doesn't replace the configuration, it appends it.
If you delete the startup-config and reload the router, the router will automatically enter setup mode. You can also type setup from privileged mode at any time.
What is the problem with an interface if you type show interface serial 0 and receive the following message?
"Serial0 is administratively down, line protocol is down."
If an interface is shut down, the show interface command will show the interface as administratively shut down. (It is possible that no cable is attached, but you can't tell that from this message.)
