Which of the following statements about the cost of capital is CORRECT? Select one: a. A company's target capital structure does not affect its weighted average cost of capital. b. The cost of retained earnings should be zero because there is no direct cost associated with capital raised as retained earnings. c. Weighted average cost of capital calculations should be focused on the after-tax costs. d. WACC should be calculated based on the book value instead of the market value. e. WACC should be calculated based on the historical costs instead of the marginal costs