In Their Study of Gratitude, Emmons and McCullough Assigned Students

In their study of gratitude, Emmons and McCullough assigned students to grateful, hassles, or events conditions. Based on the results of their study, these researchers concluded that grateful expressions

A) are helpful for people in relatively good physical and mental health, but not for people suffering serious illness (as shown in their study of people with neuromuscular disease) .
B) enhance well-being only if they are both appreciated and reciprocated.
C) coupled with downward social comparisons have the strongest positive effects on well-being.
D) may contribute to an upward spiral of well-being as described by Fredrickson's broaden-an-build theory of positive emotions.