Which of the Following Statements Is Correct

Multiple Choice

Which of the following statements is correct?

A) In the long run, both perfectly competitive firms and monopolistically competitive firms operate with excess capacity.
B) A firm operates with excess capacity when, in the long run, its level of output is below the efficient scale.
C) For any firm, efficient scale is the level of output at which the average-total-cost curve is tangent to the demand curve.
D) All of the above are correct.