The manufacturers of several designer purses have met and agreed not to sell their purses to Jolie's Department Store because of Jolie's practice of discounting all items 20 percent below the retail costs at other stores. The manufacturers are concerned about maintaining their images of exclusivity and quality. The agreement among the manufacturers: a. is valid because of their need to protect their product. b. violates the Sherman Act because it is a boycott. c. is valid because the rule of reason applies and they have a valid reason. d. none of the above