A binding price ceiling causes a shortage in the market

In a competitive industry some firms earn positive economic profits while some earn zero economic profit in the long run because:

A) there exists free entry and exit of firms. B) the firms have different cost structures. C) the firms sell their output at different prices. D) the industry supply curve is perfectly elastic.

Which of the following will not generally be true of a monopolistic competitor operating in the long run?

a. marginal cost exceeds average total cost b. marginal revenue = marginal cost c. production in the range of economies of scale d. price greater than marginal revenue