Which one of the following instigates a SYN flood attack?

A SYN attack occurs when an attacker exploits the use of the buffer space during a Transmission Control Protocol (TCP) session initialization handshake.The attacker floods the target system's small "in-process" queue with connection requests, but it does not respond when a target system replies to those requests.This causes the target system to time out while waiting for the proper response, which makes the system crash or become unusable.