Final answer:
Computers requesting hypermedia documents on the Internet are called clients. They send requests to servers for content, as opposed to hubs or switches, which manage data flow, or servers, which provide content.
Step-by-step explanation:
Computers requesting hypermedia documents on the Internet are referred to as clients. These clients make requests to servers, which are systems that store and deliver the content of hypermedia documents. To clarify, hubs and switches are networking devices that help manage data flow in a network, but don't request hypermedia documents. Servers, on the other hand, are the providers of hypermedia documents and respond to the requests made by clients. Therefore, the correct answer is d. clients.