Answer:
A. postconventional level
Step-by-step explanation:
In the postconventional stage of morality (the final stage of moral development), the person has found, by own experience and judgement, a series of abstract, general, moral principles, that he or she applies whether they coincide with social conventions or not.
In the case of the lifeguard, the social convention is to respect the orders of his boss, and only do what he is allowed to do in his job. However, in his individual, abstract reasoning, saving a person's life is more important than keeping his job, therefore, he decides to disobey his boss, save the man's life, and assume the consequences.