Refer to the exhibit.

An IP phone that is connected through a Cisco Catalyst 3750 Series Switch is failing to register
with Cisco Unified Communications Manager. When the user presses the settings button on the
phone, the Operational VLAN ID shows a blank entry. What is the most likely cause for this issue?

A.
The switch may not be supplying inline power.

B.
The spanning tree portfast command needs to be removed.

C.
The trunk encapsulation is missing. The trunk must be configured for dot1.Q.

D.
Cisco Discovery Protocol is disabled on the switch

E.
The Operational VLAN ID of the phone always shows as blank. The Admin VLAN ID should be
110.