In an Effort to Get His Dog to Roll Over

In an effort to get his dog to roll over, Bronn gives his dog a treat if he turns to the left. After the dog is reliably turning left, he must get down on the ground to get another treat. Then again he has to roll left for the treats. Finally the dog has to roll over to get a treat. Bronn is using the method known as

A) higher-order conditioning
B) punishment
C) backward pairing
D) shaping
E) classical conditioning