Answer:
d. behavioral; brain
Explanation:
The facial-feedback hypothesis was pioneered by William James and Charles Darwin but their hypothesis was not a proven hypothesis or theory, it is a conjecture.
According to the facial-feedback hypothesis, the contraction or the physical expression of the facial muscles tries to communicate what a certain individual feels for some other person. It also reveals oneself about how one feels about others.
In the context, the smile is a behavioral component of our emotion as when we smile, the facial muscles on our face sends a signal to the brain that determines the emotions we experience.
