Andrew feels good about himself. He doesn't know exactly why he is so happy, but every day he looks forward to his schoolwork and chores. "I play a game," he says. "I make a list of everything I have to get done, and then I try to finish it all before a certain time. For some reason, I feel great when I beat my time." Based on this information, why is Andrew happy?
A. He gets a proper amount of sleep
B. He eats healthy meals
C. He has a strong family support group
D. He regularly meets his own goals