A basic assumption of Freud's psychoanalytic theory is that:

A. Free association is the key to understanding: Free association is a technique in psychoanalysis but not a basic assumption of the theory. B. Sexuality does not relate to behavior: Freud's theory emphasizes the role of sexuality in behavior. C. All human behavior is caused and can be explained: Correct. Freud believed that all behavior is determined by unconscious motivations and can be understood through psychoanalysis. D. Human behavior is entirely unconscious: Freud acknowledged conscious behavior but emphasized the role of the unconscious.