设 $A$ 为 3 阶矩阵, $P$ 为 3 阶可逆矩阵, 且 $P ^{-1} A P =\left(\begin{array}{lll}1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 2\end{array}\right)$, 若 $P =\left( \alpha _1, \alpha _2\right.$, $\left.\alpha _3\right), Q =\left( \alpha _1+ \alpha _2, \alpha _2, \alpha _3\right)$, 则 $Q^{-1} A Q =$
A. $\left(\begin{array}{lll}1 & 0 & 0 \\ 0 & 2 & 0 \\ 0 & 0 & 1\end{array}\right]$.
B. $\left(\begin{array}{lll}1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 2\end{array}\right)$.
C. $\left(\begin{array}{lll}2 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 2\end{array}\right)$.
D. $\left(\begin{array}{lll}2 & 0 & 0 \\ 0 & 2 & 0 \\ 0 & 0 & 1\end{array}\right)$.