I just took this exam.
The author is going on the principle that if observational evidence is consistent with two theories, the more superior theory is the simpler theory. Answer choice D is stating that, saying that the inferior theory is the more complex theory.
A) This statement is too strong.

This argument isn't based on one theory being true and one being false which rules this answer choice out.
C) The stimulus isn't talking about the more "intuitively true" theory being the better theory. It's the theory that is more simple.
E) It's talking about which theory is more important which is not the basis on how they arrived at which theory is better.