Which pre-conditions must be met before an OSPF router can perform graceful restart？（）

A.Router must be ABR
B.Router must contain one sham link.
C.The network topology must be stable.
D.Router must be able to forward packets.
E.Neighbors must support graceful restart.

A.area 0.0.0.0{ linkneighbor-id 172.168.18.2 transit-area 0.0.2.1；}
B.area 0.0.0.0{ virtual-linkneighbor-id 172.168.18.2 transit-area 0.0.2.1；}
C.area 0.0.0.1{ virtual-linkneighbor-id 172.168.18.2 transit-area 0.0.2.1；}
D.area 0.0.2.1{ virtual-linkneighbor-id 172.168.18.2 transit-area 0.0.0.0；}

A.Choose the lowest primary address.
B.If assigned，always choose address of fxp0.
C.Choose numerically highest IP address of lo0.
D.Choose numerically lowest IP address of fxp0.
E.Choose the non-127.0.0.1 primary address on lo0.