Which of the following statements is CORRECT? a. If a firm has enough retained earnings to fund its capital budget for the coming year, then there is no need to estimate either a cost of equity or a WACC. b. A cost should be assigned to retained earnings due to the opportunity cost principle, which refers to the fact that the firm's stockholders would themselves expect to earn a return on earnings that were paid out rather than retained and reinvested. c. Suppose a firm has been losing money and thus is not paying taxes, and this situation is expected to persist into the foreseeable future. In this case, the firm's before-tax and after-tax costs of debt for purposes of