Eileen goes to a therapist for help in losing weight. She and her therapist develop a written agreement spelling out weekly step-by-step methods for Eileen to use in order to reach her weight goal. The plan specifies rewards for reaching weekly goals and penalties for not achieving them. Eileen's therapist is using which of the following methods?

A) a token economy
B) desensitization
C) classical conditioning
D) a contingency contract