A nurse is discussing Freud's psychoanalytic theory with a patient undergoing psychotherapy. According to Freud, which part of the personality operates based on the reality principle and mediates between instinctual desires and societal rules?

Rationale: A. The unconscious is a level of awareness, not a structural part of the personality. B. The id operates on the pleasure principle, seeking immediate gratification of instinctual drives. C. The ego functions on the reality principle, mediating between the impulsive demands of the id, the moral constraints of the superego, and the realities of the external world. D. The superego represents internalized moral standards and ideals but does not mediate between impulses and reality—that is the ego's role.