矩阵 $\left( \begin{array}{lll}1 & a & 1\\ a & b & a\\ 1 & a & 1 \end{array} \right)$ 与 $\left( \begin{array}{lll}2 & 0 & 0\\ 0 & b & 0\\ 0 & 0 & 0 \end{array} \right)$ 相似的充分必要条件为（ (A) $a = 0, b = 2$ . (B) $a = 0, b$ 为任意常数. (C) $a = 2, b = 0$ . $(\mathrm{D})a = 2,b$ 为任意常数