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.