Which statement is true about SYN cookies?

Which statement is true about SYN cookies?

A.
SYN cookies do not help to protect against SYN flood attacks.

B.
State is kept on the server machine TCP stack.

C.
A system has to check every incoming ACK against state tables.

D.
No State is kept on the server machine state and is embedded in the systems Initial Sequence Number (ISN).