All else constant, which of the following will increase the aftertax cost of debt for a firm?
I. increase in the yield to maturity of the firm's outstanding debt
II. decrease in the yield to maturity of the firm's outstanding debt
III. increase in the firm's tax rate
IV. decrease in the firm's tax rate
A. I only
B. I and III only
C. I and IV only
D. II and III only
E. II and IV only