Refer to the exhibit. 
A user is on a call to the PSTN through the MGCP gateway at BR1. The
gateway and the IP phone lose the connection to the Cisco Unified CallManager cluster at HQ and
the call is dropped. What is causing the call to be dropped?
A.
The CallManager cluster has lost control of the D channel on the PRI gateway at BR1.
B.
SRST has not been configured on the BR1 gateway.
C.
The IP phone has not registered with SRST.
D.
The no h225 timeout keepalive command has not been configured on the gateway.