One difference between the short run and the long run is that perfectly competitive firms: a. always earn more economic profit in the long run. b. always earn positive economic profit in the short run, but never in the long run. c. can earn positive, negative, or zero economic profit in the short run, but will earn zero economic profit in the long run. d. earn zero economic profit in the short run, but will earn positive economic profit in the long run.

The correct answer is option c.

Explanation:

In case of perfect competition there is no restriction on entry or exit for firms in the long run. Though in the short run firms can not enter or exit.

The firm's may have positive, negative or zero economic profits in the short run based on their cost conditions.

But in the long run firms will always have zero economic profits. If there is negative profits in short run the firms incurring losses will exit in the long run. This will go on till profits is zero.

In case there is positive profits, new firms will enter the industry increasing supply. This will lead to a fall in price and consequently profits will be reduced. This will go on till profits become zero.

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