Why is it often easier to start a fitness program than it is to maintain one? a. the motivation at the start of a program is often higher than later on when the progress made might be less obvious. b. at the start of a fitness program, the body is less used to physical activity so it feels better. c. maintaining a fitness program decreases an individual's ability to sleep, making it more difficult to maintain a program than to begin one. d. all of the above