When all firms and potential firms in a market have the same cost curves, the long-run equilibrium of a competitive market will free entry and exit will be characterized by firms

A. Earning small but positive economic profits.

B. Facing the prospect of future losses.

C. Operating at the efficient scale.

D. That work together to raise market prices.

The correct answer would be C) operating at efficient scale.

Explanation:

When the firms have same cost curve in the market, where there is free entry and exit, then the firms in the market must be earning zero economic profit which is when price of good is equal to total average cost of production.

For example if firms in market are profitable, then new firms would want to enter the market and when they do there will be increase in quantity of goods, so the prices and profit would go down. And if the situation was opposite, when firms are not profitable in market, then many firms will exit the market, which will lead to decrease in quantity of goods and increase in prices and profits.

So in the long run equilibrium, all firms would be operating at the efficient scale.