The correct answer is D. Web Browsers.
A web browser is a software application that allows users to access and view web pages on the Internet. It is a navigable window into the Web because it allows users to click on hyperlinks to navigate between web pages.
Hypertext is a system of non-sequential writing that allows the user to jump from one point in a document to another. It is used on the World Wide Web to create hyperlinks that allow users to jump from one web page to another.
A network is a group of computers that are connected together so that they can share information and resources. The Internet is a global network of computers that allows users to connect to each other and access information from anywhere in the world.
None of these is the correct answer because they are not programs that serve as navigable windows into the Web.