How can Fred accomplish this?

Fred is the network administrator for his company. Fred is testing an internal switch.

From an external IP address, Fred wants to try and trick this switch into thinking it already has established a session with his computer.

How can Fred accomplish this?
A . Fred can accomplish this by sending an IP packet with the RST/SIN bit and the source address of his computer.
B . He can send an IP packet with the SYN bit and the source address of his computer.
C . Fred can send an IP packet with the ACK bit set to zero and the source address of the switch.
D . Fred can send an IP packet to the switch with the ACK bit and the source address of his machine.

Answer: D