The correct answer is letter B
Explanation: Placebo is a treatment that has no action against a symptom or disease, but often leads to healing.
Used primarily in research control groups, they are critical for evaluating the effects of a given drug. When we use placebos in experiments, we expect that the group using it will not show any clinical improvement. The group that is using the real drug, on the other hand, should show a substantial improvement, thus representing the therapeutic efficacy of a new drug.
