Which of the following statements about the cost of capital is correct? Select one O a WACC should be calculated based on the book value instead of the market value Ob. The reason we must assign a cost of capital to retained earnings involves the opportunity cost principle OcWeighted average cost of capital calculations should be focused on the before-tax costs Od. WACC should be calculated based on the historical costs instead of the marginal costs. Oe. A company's target capital structure does not affect its weighted average cost of capital