In the Long Run, Neither Competitive Price Takers nor Competitive

In the long run, neither competitive price takers nor competitive price searchers will be able to earn economic profits because

A) entry barriers into these markets are high, raising the costs of each firm.
B) the government will dictate moderate prices for these firms.
C) competition will force prices down to the level of per-unit production costs.
D) marginal revenue is always less than marginal cost when barriers to entry are low.