Which of the following statements is CORRECT?

a. Since the money is readily available, the after-tax cost of retained earnings is usually much lower than the after-tax cost of debt

b. All else equal, an increase in a companys stock price will increase its marginal cost of new common equity, re

c. All else equal, an increase in a companys stock price will increase its marginal cost of retained earnings, rs

d. When calculating the cost of preferred stock, a company does not need to adjust for taxes, because preferred stock dividends are not deductible by the paying corporation