A.Because Frame Relay IETF encapsulation is only configurable at interface level， you must use IETF encapsulation on all routers.
B.This is not a possible scenario. A dedicated Frame Relay link to RemoteB is mandatory at the central office.
C.The router at RemoteB must be replaced by a Cisco router.
D.Use Frame Relay IETF encapsulation on a per-VC basis on the central office router.
E.There is a problem in the Frame Relay cloud， because Cisco routers are compatible with IETF Frame Relay.