Level I: preconventional morality. Stage 2: the purpose and exchange (individualism).
What characterizes stage is the concrete individualism, what is right at this stage is to follow the norm only when it benefits someone, act in favor of one's own interests and let others do it too.
The reason for doing the right thing is to satisfy one's needs in a world in which one has to recognize that others also have their needs and interests.
The answer is: a. preconventional level.