Answer:
C. The placebo effect
Step-by-step explanation:
The placebo effect: It states that some people experience gain after fake treatment or the application of an inactive substance. The placebo substances have no medical effects, for example, a sugar pill, sterile water, and saline solution. The people getting placebo treatment believe that they are getting real treatment and show improvement, and hence placebo effect occurs. This is being used in blind and double-blind studies. It also occurs in day to day life.