Which of the following statements is most correct? a. because the cost of debt is lower than the cost of equity, value-maximizing firms maintain debt ratios of close to 100%.b. corporations that are 100% equity financed will have a much lower weighted average cost of capital because the lack of debt lowers their risk of bankruptcy. c. the source of capital with the lowest after-tax cost is preferred stock, because it is a hybrid security, part debt and part equity. d. the cost of a particular source of capital is equal to the investor's required rate of return after adjusting for the effects of both flotation costs and corporate taxes.