why do single firms in perfectly competitive markets face horizontal demand curves? a. with many firms selling an identical product, single firms have no effect on market price. b. with many buyers, single firms can sell as much as they want regardless of price. c. with many firms in the market selling a differentiated product, single firms have the ability to charge a constant price. d. with each firm facing a unique demand for its product, single firms have no effect on market price.
