The Reason That Firms Cannot Charge More Than the Market

The reason that firms cannot charge more than the market price for a product in perfectly competitive markets is that:

A) one firm's product is a perfect substitute for another firm's product.
B) there are a limited number of sellers to choose from in perfectly competitive markets.
C) firms have imperfect information about the pricing by other firms.
D) firms sell goods that are all slightly differentiated from each other.