Answer:
E. reward himself just before going to the gym
Step-by-step explanation:
To increase his likelihood of going to the gym, Carlos should reward himself just before going to the gym because it will trigger and motivate him to go to the gym which is why it's important for someone to reward him/her self after completing a key task or before starting a key task because by rewarding one own self in the moment it help the person brain to elicits positive emotions which lead to the realization that the person efforts result in a positive reward.
Therefore if Carlos wants to lose weight he should reward himself just before going to the gym which will inturn helps to increase his likelihood of going to the gym.