In a Longitudinal Study, Diener and His Colleagues Examined the Relationship

In a longitudinal study, Diener and his colleagues examined the relationship between the positive emotions (cheerfulness) of entering college freshmen and their incomes after graduation. The results of their study showed

A) cheerfulness was unrelated to later income; college grades were much more important.
B) cheerful students tended to socialize and party too much and earned lower incomes than more serious students.
C) parents' income was the most significant predictor of students' post- graduate income; cheerfulness made no difference.
D) the more cheerful students were as freshmen, the more they earned after graduation, but this effect was mediated by their parents' income.