Marcus has decided to volunteer for Habitat for Humanity this summer. He has come to realize that he is very lucky. He wants to give back to people who are not as fortunate. Marcus had probably reached the stage of moral development.

The answer is postconventional.

Explanation:

During this stage, people have well-defined moral standards, but they acknowledge those might be different from other people's. For this reason, their principles are subject to questioning and debate.

A person who has reache the postconventional stage believes there are universal values, such as justice and equality, and base their principles on these ideals.