Which of the Following Statements Is True

Which of the following statements is true?

A) The marginal entrant in a market earns the highest profit.
B) The marginal entrant has the lowest cost among all the firms in a market.
C) Differences in technology and experience can lead to firms having different costs even under perfect competition.
D) In a market that has identical cost structures for all firms, there is a possibility of positive economic profits in both the short run and the long run.