设 $\boldsymbol{A}=\left(\begin{array}{rrr}1 & 2 & -2 \\ 2 & 1 & 2 \\ 3 & 0 & 4\end{array}\right), \boldsymbol{\alpha}=\left(\begin{array}{l}a \\ 1 \\ 1\end{array}\right), \boldsymbol{A} \alpha, \boldsymbol{\alpha}$ 线性相关, 则 $a=$
$\text{A.}$
$\text{B.}$
$\text{C.}$
$\text{D.}$