A competitive firm has been selling its output for $20 per unit and has been maximizing its profit, which is positive. Then, the price rises to S25, and the firm makes whatever adjustments are necessary to maximize its profit at the now-higher price. Once the firm has adjusted, its :______________.
a. quantity of output is higher than it was previously.
b. average total cost is higher than it was previously.
c. marginal revenue is higher than it was previously.
d. all of the above are correct.