According to the scenario, the most appropriate answer is option (D) because the firewall can be defined as the software program which checks through the network for incoming and outgoing communication on predefined rules.
while the other options are wrong because of the following reasons :
A sniffer can be defined as the program which is used to check the network traffic but it didn't work on predefined rules.
An auditor can be defined as a program that is used to analyze the network.
The hacker can be a person who hacks the system to gain access or gather information.
