Dr. Barstow is treating a young man who is afraid of dogs. One method he uses is progressive muscle relaxation using vivid imagery

Once the patient is relaxed, Dr Barstow introduces the patient to a picture of a dog with instructions to "Breathe deeply and remain calm and relaxed." Which learning principle established by Wolpe is being employed in this example?
A) Mindfulness
B) Negative reinforcement
C) Backward chaining
D) Reciprocal inhibition

D