M&M Proposition I with taxes is based on the concept that: a.the optimal capital structure is the one that is totally financed with equity. b.the capital structure of a firm does not matter because investors can use homemade leverage. c.a firm's WACC is unaffected by a change in the firm's capital structure. d.the value of a firm increases as the firm's debt increases because of the interest tax shield. e.the cost of equity increases as the debt-equity ratio of a firm increases