单项选择题

A. Stateful Switchover for Cisco Nonstop Forwarding only works with BGP.
B. Stateful Switchover for Cisco Nonstop Forwarding must be configured on all adjacent routers.
C. Cisco Nonstop Forwarding with Stateful Switchover helper mode is not supported on the adjacent router.
D. Cisco Nonstop Forwarding with Stateful Switchover helper mode for OSPF has been promiscuousstandardized and is supported on the adjacent router.