Answer:
B. Chat
Explanation:
A. Antivirus is a program that runs on your computer and prevents it from being infected by stuff encountered on the Internet.
B. Chat is a messaging service that uses the Internet to work. It's not a classical Internet service like the Web or email, but that's the closest thing in your answer choices.
C. A Firewall is another form of protection from the Internet, it blocks certain communications, but a firewall is not a service and it's not Internet-based.
D. Router is a machine that directs traffic between computers, not a service.
