Which Unifying Theme in Psychology Is Best Reflected by the Observations

Which unifying theme in psychology is best reflected by the observations that both the setting in which a psychoactive drug is taken,and an individual's expectations influence the drug's effect

A)  Behaviour is shaped by cultural heritage. 
B)  People's experience of the world is highly subjective. 
C)  Psychology evolves in a sociohistorical context. 
D)  Behaviour is determined by multiple causes.