In the remote disaster recovery scenario, when the master node (U1981) fails, POTS user A of a branch node (The branch site equipment is U1911). If you make an outgoing call to the local PSTN user B through the branch node, the network element through which the SIP signaling of the call passes is ().
A . U1911->Preparation U1981->U1911
B . Prepare U1981->U1911
C . U1911
D . U1911->Main U1981->Backup U1981->U1911
Answer: A