An investor purchases one municipal bond and one corporate bond that pay rates of return of $8\%$ and $10\%,$ respectively. If the investor is in the $20\%$ tax bracket, bis after$-$tax rates of return on the municipal and corporate bonds would be$,$ respectively, A$)8\mathrm{.}00\%$ and $10\%$ B$)8\%$ and $8\%$ C$)6\mathrm{.}4\%$ and $8\%$ D$)6\mathrm{.}4\%$ and $10\%$ E$)10\%$ and $10\%$