How can the established keyword in an ACL entry be used?

How can the established keyword in an ACL entry be used?
A . to permit only the returning TCP packets from an already existing TCP connection, and deny the initial TCP packet of a new session from an untrusted network
B . to permit both the initial TCP packet of a new session and the returning TCP packets from an existing TCP connection
C . to permit only the initial TCP packet of a new session
D . to change a router into a true stateful firewall controlling the access on a session-by-session basis

View Answer

Answer: A