An engineer must configure a ACL that permits packets which include an ACK In the TCP header. Which entry must be Included In the ACL?

The `tcp-ack` keyword is not a valid or standard command syntax for specifying the ACK flag in Cisco IOS extended ACLs.

Access-list `10` is a standard ACL, which cannot inspect TCP header flags or port numbers; it only filters based on source IP address. Also, `tcp-ack` is an invalid keyword and `ip` as the protocol type is incorrect when specifying TCP flags.

Access-list `10` is a standard ACL, which cannot inspect TCP header flags or port numbers. Therefore, the `established` keyword cannot be used with a standard ACL.

The `access-list 110` indicates an extended ACL, which is necessary to inspect TCP header flags. The `established` keyword in a Cisco extended ACL specifically permits TCP packets that have the ACK or RST bit set, which is characteristic of an established TCP connection or a response to an initial SYN. This correctly identifies packets that include an ACK in the TCP header.