How is IP address spoofing detected?

Q. How is IP address spoofing detected?

A.            Installing and configuring a IDS that can read the IP header

B.            Comparing the TTL values of the actual and spoofed addresses

C.            Implementing a firewall to the network

D.            Identify all TCP sessions that are initiated but does not complete successfully

Answer: Comparing the TTL values of the actual and spoofed addresses