Final answer:
The correct answer is a) Port number. A port number is used to identify a program or service running on a computer in order to communicate over the network.
Step-by-step explanation:
The correct answer is a) Port number. A port number is used to identify a program or service running on a computer in order to communicate over the network. It is like a virtual door through which data can flow in and out of a computer. For example, when you access a website, your web browser uses port 80 for HTTP or port 443 for HTTPS.