Answer:
B. Laboratory.
Step-by-step explanation:
A drug laboratory is the best healthcare subject that can best explain how a pharmaceutical drug works, because they are the responsible for creating it.
Medical laboratories are specialized in clinical pathologies, they carry out researches about them, and try to find a possible solution, which is a drug. So, you can see it as the applied science to innovate and treat a wider range of disease, offering treatments and prevention. Actually, in most of the cases, the clinical decision is base on a laboratory study, that's why option B, a laboratory, is the best to explain the function of a specific drug, pros, cons, side effects, and more.