A profit-maximizing firm in a competitive market is currently producing 200 units of output. It has average revenue of $9 and average total cost of $7. It follows that the firm's
a. average total cost curve intersects the marginal cost curve at an output level of less than 200 units.
b. average variable cost curve intersects the marginal cost curve at an output level of less than 200 units.
c. profit is $400.
d. All of the above are correct.