设 $\boldsymbol{A}^{-1}=\left(\begin{array}{cc}1 & 2 \\ 3 & -1\end{array}\right), \boldsymbol{B}^{-1}=\left(\begin{array}{cc}2 & -1 \\ 1 & 2\end{array}\right)$ ，则 $(\boldsymbol{A} \boldsymbol{B})^{-1}=$
$\text{A.}$
$\text{B.}$
$\text{C.}$
$\text{D.}$
$\text{E.}$
$\text{F.}$