Janine was very active throughout her early adulthood and maintained a very high fitness level. If she wants to maintain this fitness level throughout her middle adulthood, how might her participation in physical activity and exercise be impacted?
A. Janine should reduce the amount of time she spends exercising because it is easier to maintain fitness levels as you age.
B. Janine should keep her current exercise program because, once a high level of fitness is reached, it never changes.
C. Janine should increase the intensity or length of her exercise programs because it is more difficult to maintain high fitness levels as you age.
 D. Janine should stop exercising completely because it is not safe for middle-aged adults to exercise.