According to longitudinal studies in both the United States and China, children who were more successful in social interactions with their peers

a. had higher than average emotional competence in infancy.
b. had higher than average emotional competence at age 3-4 years and expressed more positive and negative emotions with peers.
c. had higher than average emotional regulation but not emotional knowledge at age 3-4 years.
d. none of the above

Answer: b. had higher than average emotional competence at age 3-4 years and expressed more positive and negative emotions with peers.