He fundamental building block in every hypertext markup language (html) document is the tag, which marks a component in the document.

Complete Question: The fundamental building block in every Hypertext Markup Language (HTML) document is the tag, which marks a component in the document.

The Element Tag

Explanation:

In Hypertext Markup Language, the element tag which has an "open and closing"  (With a few exceptions with only opening tags e.g the break tag that produces a new line) is considered the fundamental building block of an HTML document. There exist elements for representing every component of an HTML document, Headings, Title, paragraphs, body, etc. Each of these elements used in their respective tags represents the appropriate section/component of an HTML document.

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