A professor conducts an experiment in which she asks her students to either hold a pen between their teeth or between their lips. Holding the pen between one's teeth mimicked the facial expression of smiling. After five minutes, she finds out that the students who held the pen beneath their teeth reported being happier than those who held it between their lips. These results most likely support the
a) facial feedback hypothesis
b) Schachter-Singer theory
c) two-factor theory of emotion.
d) Cannon-Bard theory