Can you explain all the answer choices?

same

I think the point of the second paragraph, and of this sentence in particular, was to show that the type of research in question required multiple sets of skills, and that the overlap between the sets of skills was virtually nonexistent. This is a good for form D, the author was trying to show that the experts in two two fields did not coincide. While this likely could have been a possible motivator, the author does not really tell us that this lack of overlap was a motivating factor.