设 $A$ 为3阶矩阵， $P$ 为3阶可逆矩阵，且 $P^{-1}AP = \begin{pmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 2 \end{pmatrix}$ . 若 $P = (\alpha_{1},\alpha_{2},\alpha_{3})$ ， $Q = (\alpha_{1} + \alpha_{2},\alpha_{2},\alpha_{3})$ ，则 $Q^{-1}AQ = (\quad)$ (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) $\left( \begin{array}{lll}2 & 0 & 0\\ 0 & 2 & 0\\ 0 & 0 & 1 \end{array} \right)$