Âthe first line in a hypertext markup language (html) file is the which is a processing instruction indicating the markup language used in a document.

The first line in a hypertext markup language (html) file is the Doctype, which is a processing instruction indicating the markup language used in a document.

The correct answer is:

Doctype

Explanation:

The Doctype is the abbreviation for document type declaration which is an instruction related to XML and SGML documents that makes them adopt a document type definition to be shown as an element compatible in that format. In other words, it allows them to be from one type and be translated into another type without visual or presentation modification. It is just to be more flexible, fast, and manipulable.