An external call is dropped as soon as it is picked up by the SCCP IP phone, the PSTN gw is integrated with CUCM using a SIP trunk. What is a cause of this issue?

A.	there are insufficient DSP resources on the PSTN gw
B.	there is a missing MTP resource for the SCCP IP phone
C.	the incorrect CSS is on the SIP trunk to the PSTN gw
D.	the phone number is in the incorrect partition