Which Ought to Be More Fundamental, the Hypothesis or the Explanandum

Which ought to be more fundamental, the hypothesis or the explanandum?

A) The hypothesis when the explanation provides a cause, but the explanandum when it provides a reason.
B) The hypothesis when the explanation provides a reason, but the explanandum when it provides a cause.
C) The two should be equally fundamental.
D) Always the explanandum.
E) Always the hypothesis.