Which of the following statements about the cost of capital is INCORRECT ?

Select one:

a.Weighted average cost of capital calculations should be focused on the before-tax costs.

b.The reason we must assign a cost of capital to retained earnings involves the opportunity cost principle.

c.WACC should be calculated based on the market value instead of the book value.

d.A company's target capital structure affects its weighted average cost of capital.

e.WACC should be calculated based on the marginal costs instead of the historical costs.