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.