Which of the following explains why a monopolistically competitive firm that earns a short-run economic profit would earn only a normal profit in the long run?

• A - New firms will be able to enter the firm's market in the long run.
• B - The firm's demand curve is downward sloping.
• C - The firm can differentiate the product is sells in the short run but not in the long run.
• D - The firm must lower the price of the product it sells in order to increase quantity demanded in the long run.
• E
• The firm's demand curve will become perfectly elastic in the long run.