Which of the following is true of marginal cost?
a. Marginal cost is the cost per unit of output produced.
b. Marginal cost curve is negatively sloped at the profit-maximizing level of output.
c. Marginal cost initially increases with an increase in output but subsequently declines.
d. Marginal cost is the change in total cost divided by the change in total output.
e. Marginal cost is equal to total cost divided by the quantity of output