Answer:
I would say the best answer for this question would be A.
Step-by-step explanation:
I chose this answer because factually, it does check out. Say, for example there is a clinical trial for a drug to treat a specific disease.
I can rule out B because obviously these doctors would not purposely infect the volunteer with this disease just to take a shot at curing them.
I ruled out C because if we were using this trial drug on a completely healthy person... how would we know that the drug can help/cure the disease in mind if the person never had the disease in the first place. C is simply absurd.
And finally, D is much like B and so I can rule it out as well for the same reason.