Which of the Following Will Increase the Competitive Efficiency of a Market

Which of the following will increase the competitive efficiency of a market?

A) Setting prices below cost such that smaller firms are driven out of the market
B) Selling products such that the consumer cannot buy one good without buying the other
C) Selling the same product at different prices to different consumers
D) Mergers between firms such that cost of production in the market is lower but price is higher.
E) Removal of prohibitive barriers to entry in the market