Final answer:
A page break is what determines when the text has filled one page and must continue on the next in a word processing document.
Step-by-step explanation:
The answer to the question is C) Page break. A page break determines when the text has filled one page and will continue on the next page according to the paper size, margin settings, line spacing, and amount of text.
In word processing software like Microsoft Word, page breaks can occur automatically when you fill a page with text or manually when you insert a break at a specific point in the document to start a new page. This feature is essential for controlling the layout of documents, especially when preparing reports, essays, or books where specific content must begin on separate pages.