An investor purchases one municipal bond and one corporate bond that pay rates of return of 8% and 9.6%, respectively. If the investor is in the 20% tax bracket, his after-tax rates of return on the municipal and corporate bonds would be, respectively, _____.

A. 8% and 9.6%

B. 8% and 7.68%

C. 6.40% and 9.6%

D. 9.6 % and 7.68%