Of the following, which is the oldest theory of personality?

A) phrenology
B) behaviorism
C) the psychodynamic approach
D) humorism

Answer: D
Rationale: Ancient medicine was guided by the theory of humorism. According to this theory, the body consisted of four humors—including blood, phlegm, black bile, and yellow bile. Physical illness and disorders of personality were attributed to imbalances among the four humors. The other theories listed were all more recently.