When Training a Dog to Perform on a Television Show

When training a dog to perform on a Television show the trainer first watches the dog's behavior,chooses one that approximates what the director has asked to have done and begins rewarding the dog every time he performs this natural behavior.Gradually the trainer changes when the reward is given altering the behavior toward the desired performance until this is what the dog does each time,in place of the natural behavior.The trainer has used __________ to train the dog.

A) tactile communication
B) imprinting
C) a fixed action pattern
D) operant conditioning
E) chemical communication