What could be the source of the problem when you encounter a situation where incoming callers to an analog FXO port on a Cisco CME system receive dial-tone only?

A.
The direct-inward-dial is improperly configured on voice port.

B.
The default-destination is improperly configured under telephony-service.

C.
The connection plar opx is improperly configured on voice port.

D.
This is default behavior for Cisco CME application and cannot be changed.