While Sigmund Freud Might Explain an Individual's Depression by Focusing

While Sigmund 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.Which of your textbook's unifying themes is illustrated by this example

A)  Heredity and environment jointly influence behaviour. 
B)  Psychology evolves in a sociohistorical context. 
C)  Psychology is empirical. 
D)  Psychology is theoretically diverse.