Suppose input prices rise as industry output expands. What will be the likely effect on a perfectly competitive firm's marginal cost and average cost curves?

a. They will shift upward.

b. They will shift downward.

c. They will NOT shift. As the firm increases production, however, costs increase as the firm moves upward to the right along these curves.

d. They will NOT shift. As the firm increases production, however, costs decrease as the firm moves downward to the left along these curves.