Answer: a. the participants receiving the placebo.
Step-by-step explanation:
Placebo-controlled studies are a method of experimental testing in which, thereĀ“s a group of subjects that are given the treatment under evaluation, and the control group gets a placebo treatment that is specially created to have no actual medical effect. The placebo group meant to account for the placebo effect and is required to provide comparable data to analyze whether the treatment works.