which physician was noted for his research and description of the teeth's root systems?  

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? he gets a proper amount of sleep he eats healthy meals he has a strong family support group he regularly meets his own goals