The So-Called Norm of Reciprocity Rule Makes Which of the Following

The so-called norm of reciprocity rule makes which of the following predictions?

A) Buyers will void their offers when the seller makes a concession (for instance, by coming down from her original price) .
B) When sellers start out low, buyers are less likely to buy out of fear of deception.
C) Buyers who "low ball" sellers by starting the bargaining out at a price far below asking price are most likely to prevail.
D) If I sell my car to your sister at a good price, you are likely to return the favor some day in the future.