Which of the Following Is True for a Profit-Maximizing Firm

Multiple Choice

Which of the following is true for a profit-maximizing firm operating in a competitive market,monopolistic competition,and monopoly?

A) Firms earn positive economic profits in the long run.
B) Firms earn zero economic profits in the long run.
C) Profits are maximized when marginal cost equals marginal revenue.
D) Price equals marginal revenue.
E) Entry into the industry is impossible.