The question implies that some medical colleges have decided to add research project as a part of students curriculum.
They say that this is in response to requests from public to have more thoroughly educated doctors and not an attempt to generate income from tuition. However, author feels this claim is inaccurate as there are better ways (patient-based learning) to produce more thoroughly trained doctors than by research projects.
The question asks us to strengthen the colleges' claim that this altercation is indeed in response to public requests and not an attempt increase income.
The answer should also explain why the research project is a better choice than the more obvious patient based learning approach. Once you know what the answer is supposed to do, the goal is clear.
Now lets look at the options:
A. Talks only about a doctors reputation and how he is perceived by his patients when the doctor has done some research in the past. This is slightly out of scope for the argument. At best, this just explains why the medical colleges chose research projects. It does not talk about its advantages over patient based learning.
OUTB & C. Again, does not explain the medical colleges decision.
OUTD. This option seems a very good candidate. It explains very clearly why the colleges might have chosen the research projects as an approach over patient based learning.
KEEPE. Again, the argument has no mention about how much time the research projects will take and if that is relevant in any way to making the choice to produce thoroughly trained doctors.
OUTHence it should be
D.