If you hear the prompt "The number you dial does not exist" when call an inner-office user, the possible reason is (). (Multiple Choice)

If you hear the prompt "The number you dial does not exist" when call an inner-office user, the possible reason is (). (Multiple Choice)
A . The maxlength of the corresponding inter prefix is set too short.
B . Trunk fault.
C . The dialed number is not configured.
D . U1900 MTU board fault.

Answer: AC