Which of the following does Word insert to mark a spot where a citation needs to be completed?

In Word, a placeholder is utilized to indicate where additional information, such as a citation, needs to be added later. When you insert a placeholder, it serves as a visual cue that emphasizes the need for further content in that specific area. This is particularly useful in the writing and editing process, allowing authors to track where citations or additional details must be incorporated without disrupting the flow of the document.

Comments, on the other hand, typically provide feedback or suggestions related to specific parts of the text but do not specifically indicate incomplete citations. Footnotes are used to provide additional context or references at the bottom of a page rather than marking an incomplete citation within the main text. Highlighting text can draw attention to certain sections but does not serve as a specific marker for where a citation is needed. Therefore, a placeholder is the most appropriate tool for marking a spot where citations should be included.