Thomas gained a lot of weight because he was eating too many sweets. A psychologist suggested to Thomas that he pair the pleasant taste of sweets with the taste of something he finds unpleasant. So, Thomas put broccoli, which he hates, in his ice cream, cake, and pie. He now feels nauseated at the sight of dessert and avoids eating it. This technique is known as:.
a. flooding.
b. a token economy.
c. client-centered therapy.
d. systematic desenitization.
e. aversion therapy.