Hypertext Markup Language (HTML) is the correct answer because it is specifically designed to structure content on webpages. It uses tags to denote elements such as headings, paragraphs, links, and other types of content. XML is used for data transport and storage but is not specifically for formatting or structuring web content. Java and Python are not markup languages; they are compiled and interpreted programming languages, respectively. CSS is a stylesheet language used to describe the presentation of a document written in HTML or XML, not a markup language itself.