设 $\boldsymbol{A}$ 为 4 阶实对称矩阵, 且 $\boldsymbol{A}^{2}+\boldsymbol{A}=\boldsymbol{O}$. 若 $\boldsymbol{A}$ 的秩为 3 , 则 $\boldsymbol{A}$ 相似于( )
A. $\left(\begin{array}{llll}1 & & & \\ & 1 & & \\ & & 1 & \\ & & & 0\end{array}\right)$.
B. $\left(\begin{array}{llll}1 & & & \\ & 1 & & \\ & & -1 & \\ & & & 0\end{array}\right)$.
C. $\left(\begin{array}{llll}1 & & & \\ & -1 & & \\ & & -1 & \\ & & & 0\end{array}\right)$
D. $\left(\begin{array}{cccc}-1 & & & \\ & -1 & & \\ & & -1 & \\ & & & 0\end{array}\right)$.