Arvid didn't work very hard on his last class essay assignment, so he was relieved at first to find he'd gotten a "C" on it. But when he learned that most of his classmates had gotten "B's" and "A's", he felt unhappy and angry about his grade. Arvid's experience is best explained in terms of
A)Parkinson's second law.
B)displacement.
C)the adaptation-level phenomenon.
D)the relative deprivation principle.