Final answer:
The strategy being used in this scenario is Operant Conditioning. The student rewards their sister with a delicious chocolate treat every time she takes out the trash, which results in an increase in the behavior of taking out the trash.
Step-by-step explanation:
The strategy that is MOST likely being used in this scenario is Operant Conditioning. Operant conditioning is a type of learning where organisms associate a behavior with its consequences. In this case, the student rewards their sister with a delicious chocolate treat every time she takes out the trash, which results in an increase in the behavior of taking out the trash. The chocolate treat serves as a positive reinforcer, making the behavior of taking out the trash more likely to be repeated in the future.