What is the proper question form of 'He has been here before'?

The correct choice, which is "Has he come here before?", appropriately transforms the original statement "He has been here before" into a question while retaining the original meaning. The phrase uses the present perfect tense, which is essential in this context because it expresses an experience or occurrence relevant to the present.

When changing a statement to a question in the present perfect tense, the auxiliary verb "has" (or "have") is moved to the beginning of the question, followed by the subject "he," and then the main verb "come" in its base form. This structure is critical as it aligns with the grammatical rules governing questions in English.

The other options do not maintain the exact meaning of the original statement. While they might repurpose elements of the phrase, they diverge from the present perfect aspect or alter the intended meaning. For example, some options shift the focus to the act of coming or the timing of the visit rather than emphasizing the experience of having been there, which is central to the original statement.