Which of the Following Is an Example of Backdoor Selling

Which of the following is an example of backdoor selling?

A) Marty gave the purchasing agent a box of Cuban cigars.
B) Andrea told the members of the buying center a decidedly dirty joke.
C) When the purchasing agent wouldn't see him Billy contacted the president of the company to try to sell his product.
D) When the purchasing agent wouldn't buy his product line, Kenneth offered a new set of seat covers made out of lamb's wool.
E) Barbara reported the purchasing agent for making lewd remarks about her figure.