The answer is D: that has an undetermined answer.
Honest research —which, ideally, should be the only form of research ever undertaken— should aim at originality and authenticity in its objectives and goals, starting from questions that have not yet been answered but that, with dedication and hard-work, could be answered. A research question, being the synthesis of the research itinerary that a researcher will follow, should aspire to solve or answer a question that is still undetermined but that can be, if properly approached, answered.
