Five-year-old Will is terrified of dogs. During a therapy session, Will watches from a safe distance as another child approaches a dog with no ill effect. Then the child reaches out to pet the dog and finally holds the dog in her lap. Will is encouraged to engage in each step himself. The therapist is trying to treat Will's fear of dogs with:

A. time out.
B. token economy.
C. participant modelling.
D. psychodrama