Choice A is the best answer. The "deadweight loss" mentioned in the second paragraph is the significant monetary difference between what a gift-giver would pay for something and what a gift-recipient would pay for the same item. That difference would be predictable to social psychologists, whose research "has found that people often struggle to take account of others' perspectives—their insights are subject to egocentrism, social projection, and multiple attribution errors" (lines 31-34,"Research...errors.").
Choices B, C, and D are all incorrect becauselines 31-34 ("Research...errors.") make clear that social psychologists would expect a disconnect between gift-givers and giftrecipients, not that they would question it, be disturbed by it, or find it surprising or unprecedented.