Recently the corporate tax law in the U.S. changed so that firms that previously faced a marginal tax rate of close to 40% now pay tax at a flat rate of 21%. Holding everything else constant, this reduction in the tax rate faced by corporations ________.

A. decreased the aftertax cost of debt

B. increased the aftertax cost of debt

C. did not change the aftertax cost of debt

D. increased the value of the deduction for interest expense