When using a system on the internal network side of a NAT firewall, what would the IP addresses look like for the source and destination IP addresses in the IP header of packets being sent out of the internal network to an external host from the NAT device?

The source IP address of the packets would be the NAT firewall's internal network address.

The source IP address of the packets would be one of the NAT firewall's public addresses.

The source IP would stay as the internal IP address of the system.

The source IP address would be changed to a random address to completely obsfucate the sender$\text{'}$s real IP address.