Don Has Been Suffering from Some Intense Feelings of Anxiety

Don has been suffering from some intense feelings of anxiety and decides to seek some help from a psychotherapist. Unfortunately, there is long waiting list and the first available appointment is 9 weeks away. Disappointed, Don decides to put his name on the waiting list anyway. A few weeks pass and even though he has done nothing to address the problem, Don's anxiety symptoms begin to fade and eventually disappear. This example best demonstrates the phenomenon called:

A) insight.
B) spontaneous remission.
C) the placebo effect.
D) the deterioration effect.