If a dominant firm is charged with refusal to deal under antitrust law, it is being charged because a. it will sell its products only to people who agree to buy only from it and not from rival firms. b. the firm will not set its price at the regulated rate. c. it is refusing to cooperate with antitrust authorities, such as the department of justice. d. it is refusing to sell a key input to downstream rivals, thereby reducing or destroying competition.