Answer:
Accidental reinforcement
Step-by-step explanation:
Accidental reinforcement occurs when a reinforcer casually concurs with a positive outcome, so the person associate the outcome with the reinforcer. This type of reinforcement is usually the source of superstitious behaviours.
In this case, Roger associated the fact of wearing green underwear to the good grade he got in his test, the green underwear was the reinforcer that casually concurs with the positive outcome which in this case was the good grade, so Roger started associating both and now he wears green underwear on test days.