For the Cobb$-$Douglas utility function for two goods, $u(Q_1,Q_2)=A{Q}_1^{}{Q}_2^{}$ where $A,$ and $$ are constants. The Marginal Rate of Substitution between goods $1$ and $2,MR{S}_{12}$ is

$($a$)\frac{}{}$

$($b$)\frac{Q_2}{Q_1}$

$($c$)\frac{}{}\frac{Q_2}{Q_1}$

$($d$)\frac{}{}\frac{Q_2^{-1}}{Q_1^{-1}}$

$($e$)\frac{}{}(\frac{Q_2}{Q_1}{)}^{\frac{}{}}$