Reciprocity Is Involved in Which Situation

Reciprocity is involved in which situation?

A) agreeing to a smaller request after a person accepts your refusal to a larger request
B) agreeing to a second request after thinking a person has given us a better deal than the first request
C) agreeing to a second request for a large contribution after agreeing to make a small contribution
D) agreeing to a smaller request after a person accepts your refusal to a larger request, and agreeing to a second request after thinking a person has given us a better deal than the first request