Conceptually, which statement applies only to a market under monopolistic competition and not to a market under a monopoly?

Group of answer choices:

A firm operating in the market can make positive economic profits in the short run

None of the other answers (i.e., all of the other answers apply to both market structures)

Firms face a downward-sloping demand curve

If economic profits are being made, new firms will enter the market

A firm operating in the market maximizes profits where marginal revenue is equal to marginal cost