Bubba, a very smart German shepherd, has learned that if he barks at the neighbors while they're grilling, they will throw him a candy. However, his owner, Paul, does not want Bubba to eat candy as it is not good for his health. He does not allow Bubba to eat candies from the neighbor. When Paul is in the yard, Bubba never barks at the neighbors. According to operant-conditioning principles, Bubba is demonstrating that he can