The correct answer is B. The placebo effect
Step-by-step explanation:
The term "placebo effect" describes the use of a neutral medicine or fake treatment that might still improve the symptoms of an individual, which the result of the expectations of the individual rather than an active substance in the "medicine". This effect occurs in the case of Tracy because even if the liquid she takes is only water with green food coloring (fake medicine) her symptoms reduced, which is likely connected to her expectations and other psychological elements. Thus, this is an example of the placebo effect.