According to Kohlberg's theory of moral development, which of the following universal stages is grouped under the conventional level?

a. Follow rules only if it is in own interest, but let others do the same. Conform to secure rewards.
b. Follow self-chosen universal ethical principles. In the event of conflicts, principles override laws.
c. Obey rules to avoid punishment.
d, Conform to meet the expectations of others, please others, and adhere to stereotypical images.