Which of the following IOS features can prevent IP spoofing attacks？（）

A.Version
B.Label
C.COS/EXP
D.TTL
E.S flag

A.It adds the VPN label into the top label in the MPLS label stack
B.It replaces the top label in the MPLS label stack with a VPN label and propagates
C.It replaces the bottom label in the MPLS label stack with a VPN label and propagates
D.It removes the top label in the MPLS label stack and does a Layer 3 lookup on underlying IP packets
E.None of above