One fraternity has only 3 openings, but during pledge week, the number of pledges increases from 4 to 9. Another fraternity has 8 openings, but only 2 pledges by the end of the week. This discrepancy was likely influenced by
a. scarcity only.
b. scarcity and reactance only.
c. compliance only.
d. scarcity, reactance, and compliance.