All else constant...........(see in the pic)

24. All else constant, which of the following Will decrease the after-tax 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 firms outstanding debt III. Increase in the firm?s tax rate iv. Decrease in the firm?s tax rate A. II and IV only B. II and III only C. I and IV only D. I and III only E. I only