Which of the following statements is sequentially correct?
a. Changes in marginal physical product change marginal cost, which changes average variable and average total cost.
b. Changes in marginal cost change marginal physical product, which changes average variable and average total cost.
c. Changes in average variable cost change marginal cost, which changes average total cost, which changes marginal physical product.
d. Changes in average variable and average total cost change marginal cost, which changes marginal physical product.