The answer to this is C. There are several factors that can make a research problem well-written. First of all, the intent of the research problem should be clear. Through the main research problem, people can think about a variety of other problems that are related to it. The research problem should also be based on a theory so that the reader of the research problem will know that the problem is plausible and has a possibility of being resolved.
There are instances when research problems can be related to different fields. It should not be stuck to just one academic field. The more significant the research problem is, especially to the lives of those who are doing it, the better.