Which one of the following statements related to the M&M Propositions is correct? a. M&M Proposition I, with taxes, implies that the capital structure of a tax-paying firm is irrelevant. b. M&M Proposition I, with taxes, implies that the WACC of a firm remains constant even if the capital structure is changed. c. M&M Proposition I, with taxes, implies that WACC decreases as the debt-equity ratio increases. d. M&M Proposition II, without taxes, implies that the cost of equity remains constant as a firm increases its debt-equity ratio