Mary likes to go out on the weekends to have fun. She drinks on these occassions and her friends have grown tired of her annoying behavior when we she has had too much to drink. They stop hanging out with her on the weekends so she goes out on her own. She can go months without drinking without any side effects when her parents are in town. But we enjoys drinking on the weekends, even if her friends have decided to stop hanging out with her. Which would best classify Mary's situation

Social system morality.

Explanation:

Kohlberg developed a new model (three levels with two stages each) because he thought Piaget's was simplistic.

The social system morality stage is characterised as fulfilling social duties in order to keep the social system going and the moral jugdment as avoiding critisism by a respected authority.

In this case, Rebecca is fulfilling her social duties (not breaking the law (a social convention)) whilst avoiding the critisism. Hence, she is in the social system morality stage.