Answer :
a. On an incoming datagram from the public Internet side of a NAT, changing the destination IP address of a datagram to a new destination sending that IP datagram on to the LAN side of the NAT.
NAT or network address translation is a network protocol is used by private networks to access the internet by assigning or mapping a public IP address to the private addresses.
The host with IP address 10.0.1.19 searches for the actual destination IP address 128.119.160.183 in its private network and when it does not find it, it sends the packet to the default gateway IP address 10.0.1.25, which is where the private IP address is NATted and sent to the destination.
learn more about of NAT here
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