Megan is 16 years old and overweight. She loves junk food and chocolate. A 10-minute walk to school is her only exercise every day. Which is the best method to help Megan lose weight? A. only one meal a day and a 30-minute daily brisk walk B. a low-fat diet and a game of tennis or a brisk walk every day C. vitamin supplements and diet pills with a brisk daily walk D. rigorous daily exercise with no change in her diet