Suppose a firm in a perfectly competitive market is earning normal profits and there is an increase in demand. In the short? run, the firm earns A. an economic profit as prices fall. In the long? run, new firms will enter and prices will fall. B. an economic profit as prices rise. In the long? run, new firms will enter and prices will fall. C. an economic profit as prices rise. In the long? run, new firms will enter and prices will rise. D. an economic profit as prices fall. In the long? run, new firms will enter and prices will rise.