Which option is not a valid method to assign the lowest-order 64-bit field of an IPv6 unicast address？（）

A.ME3000
B.UBR10000
C.ASR9000
D.CRS-1
E.ME3600
F.UBR7200

A.1
B.None
C.3
D.2
E.It depends on the numbers of hops between the ingress and egress PE

A.Provider support for intra-AS and CSC scenarios
B.Uses separate signaling plane， which provides more security than IPv4
C.BGP is the preferred routing protocol for connecting two SPs
D.No requirement for a separate signaling plane