Customer X has a hub-and-spoke Frame Relay network， with a central office and two branch offices（RemoteA and RemoteB）. Each location has only one physical link to the Frame Relay cloud and RemoteB has a router that is not a Cisco router. Since the installation，there is no connectivity between RemoteB and the central office. What is a possible solution to this issue？（）

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.