Aresearcher would like to determine the effect of caffeine on memory. participants are randomly assigned to receive a caffeine pill or a sugar pill. both groups complete a recall task that assesses their memory. however, even those who received the sugar pill had a small increase in memory. this is likely due to:
a. the experimental effect
b. the correlational approach to the study
c. the placebo effect
d. the participants becoming smarter

C. The placebo effect  

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.