What is the reason for this failure?

A user reports that when receiving an inbound call on their IP Phone from the PSTN they are unable to transfer this call to another PSTN number.

What is the reason for this failure?
A . The incoming calling search space of the SIP trunk does not include the partition of the line in the IP phone
B . The gateway is configured with the wrong device pool
C . The service parameter related to Offset to Offnet Call Transfer is set to TRUE
D . The IP phone is configured with the wrong region

Answer: C