The software that lets a user, with a click of the mouse, locate, display and download text, video, audio and graphics stored on a host computer on the web is a

A web browser lets a user click to locate, display and download text, video, audio and graphics from a host on the web.

A domain is a named part of an internet address, not the software that retrieves and shows content.

A URL is the address of a resource, again not the program that fetches and displays it.

No other choice fits because the web browser is exactly this retrieval-and-display software.

The browser sends requests to servers and renders the returned media for the user.

Modern browsers also run web applications through built-in scripting engines.