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.

A.ip verify unicast source reachable-via any
B.ip verify unicast reverse-path
C.ip verify unicast reverse-path loose
D.ip verify unicast reverse-path strict