A web server is -------.

A web server is the machine — the hardware plus the server software running on it (such as Apache, Nginx, or IIS) — whose core job is twofold: hold a website's files (HTML pages, images, scripts, style sheets, or the content needed to build a page), and listen for incoming HTTP/HTTPS requests from client browsers, sending back the matching page whenever one arrives.

Only one of the four options captures both halves of that job — storing or producing content and handing it out on request — which is exactly what "a computer that stores and delivers web pages" means, so it is the definition being asked for here.

• A program that downloads files is a download manager/FTP-style client — software that pulls content onto one user's own device; it isn't built to host content for others to request.

• A type of web browser is the client program used to open and read pages (Chrome, Firefox, Edge); it requests and renders content rather than storing and handing it out.

• A protocol used for secure communication (like HTTPS/TLS) is a set of rules for encrypting and authenticating data in transit; a protocol is a communication standard, not a physical/virtual machine.

Tracing an actual page load confirms this: typing a URL sends an HTTP request across the network to a specific machine, and it is that machine which locates the stored file and returns it to the browser — the role uniquely matching a computer that stores and delivers web pages.