Refer to the exhibit. Highland Park Property Development is integrating a
Cisco Unified CallManager system with the existing PBX via an E1 QSIG trunk. After the initial configuration, no calls can be placed from IP phones to PBX phones. How can this problem be resolved?

A.
Add the command isdn contiguous-bchan to the serial interface.

B.
Change the channel selection order from descending to ascending.

C.
Add the command isdn negotiate-bchan to the serial interface.

D.
Increase the ISDN T302 timer to allow more time for call setup.