Which Statement Is Most Likely to Be Made by a Researcher

Which statement is most likely to be made by a researcher who studies pain perception from a functionalist perspective

A)  We can understand pain perception only if we understand the unconscious processes that initiate the sensation of pain. 
B)  We can study pain only by observing the outward expression of pain in response to different stimuli. 
C)  We can study pain only if all the component parts that make up the experience of pain are understood. 
D)  We can understand pain perception only if we understand the role of pain in human survival and adaptation.