Beth Really Wants to Get in Shape, but Just Can't

Beth really wants to get in shape, but just can't seem to ever get herself to the gym. An example of a commitment device Beth could use would be to:

A) spend time doing something she really enjoys, like watching a movie, before going to the gym.
B) allow herself to eat one dessert as a reward for each visit to the gym.
C) make arrangements to meet with an exercise buddy every day at the gym to work out together.
D) None of these are commitment devices Beth could use.