While Freud might explain an individual's depression by focusing on the person's unconscious thoughts, a physiological psychologist might focus instead on a chemical imbalance in the brain. This difference in explanations BEST illustrates the text's unifying theme that

a. psychology evolves in a sociohistorical context.
b. heredity and environment jointly influence behavior.
c. psychology is theoretically diverse.
d. psychology is empirical.

C