Final answer:
The dog's vocalizing behavior when left alone is positively reinforced by the owner's return.
Step-by-step explanation:
The vocalizing behavior of the dog that is left alone and increases when the owner runs back into the room is an example of D. Positively reinforced by the owner's return. In operant conditioning, positive reinforcement occurs when a behavior is strengthened by the subsequent presentation of a desirable stimulus. In this case, the dog's vocalizing behavior is reinforced by the owner's return, which is a desirable stimulus for the dog.