In a Weight-Reduction Experiment, an Overweight Individual Was Given What

Multiple Choice

In a weight-reduction experiment, an overweight individual was given what the researcher called a new type of diet pill that would help curb the desire to eat. In fact, the pill really contained powdered milk, but ever since the individual started taking the diet pill, he has reported that his desire to eat has decreased. This illustrates the

A) curvilinear relationship.
B) effect of extraneous variables.
C) natural experiment.
D) placebo effect.