设 $\boldsymbol{A}_{n \times n}$ 与 $\boldsymbol{B}_{m \times m}$ 均可逆，则 $\boldsymbol{C}=\left(\begin{array}{cc}\mathbf{A} & 0 \\ 0 & \mathbf{B}\end{array}\right)$ 也可逆，且 $\boldsymbol{C}^{-1}=$
$\text{A.}$
$\text{B.}$
$\text{C.}$
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