What could be the source of the problem when you encounter a situation where a 7910 IP phone registers is Cisco CME, but extension numbers do not appear?
A.
ephone-dn has not been mapped to ephone.
B.
An undefined phone type for 7910 under ephone.
C.
There is an authentication failure during auto-registration.
D.
Cisco CME and 7910 need to be in same device pool.