Final answer:
The server is the central node that coordinates the flow of data by sending messages directly between sender and receiver nodes in a network.
Therefore, the correct answer is server (option b).
Step-by-step explanation:
A server is a computer or system that provides resources, data, services, or programs to other computers, known as clients, over a network.
It is the central node that coordinates the flow of data by sending messages directly between the sender and receiver nodes.
It acts as the backbone of a network and manages resources, such as files, databases, and network services. It can process requests from multiple clients and send responses back to them.
For example, in a client-server model, when a client requests a webpage, the server receives the request, retrieves the webpage, and sends it back to the client. The server also ensures that the data is delivered to the intended recipient and manages the overall network traffic.