need help

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