Which two VoIP capabilities are utilized when the CallManager and the gateway are configured for Survivable Remote Site Telephony？（）

A.Analog phones， connected to the PSTN， act as internal call agents if IP communication to the CallManager is lost.

B.An onsite gateway reroutes calls over the PSTN if IP communication to the CallManager is lost.

C.The IP phones can reroute calls over the PSTN if IP communication to the CallManager is lost.

D.Local voice gateways can assume the function of a call agent if IP communication to the CallManager is lost.

E.IP phones use an internal call agent if IP communication to the CallManager is lost.