Reciprocity Is Sometimes,but Not Always,unethical Behavior

Reciprocity is sometimes,but not always,unethical behavior. Which of the following situations is an example of reciprocity which is unethical behavior?

A) An architect refuses to allow any other builders to build her designs because she doesn't trust the quality of the jobs performed by other builders. The builder does not build designs by other architects because other architects cut corners in the designs.
B) A plastics company is willing to develop a special process for coating nonstick cooking equipment. As a thank-you,the cooking equipment company allows employees of the plastics company to use the same employee discount its own employees enjoy for purchases of cooking equipment.
C) A restaurant chef buys all his produce from the local farmers' market. The farmers and workers at the market eat their meals at that restaurant on the days they sell at the market.
D) A garbage hauling service requires that a hotel chain give a discount to employees of the garbage hauling service in exchange for discounted garbage hauling services for the hotels.
E) The merchants in one neighborhood of a large city have decided to engage in a"buy local"campaign and to patronize each other whenever possible,even if they could find slightly lower prices in other areas of the city.