$\boldsymbol{A}$ 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. $\left(\begin{array}{llll}-1 & & & \\ & -1 & & \\ & & -1 & \\ & & & 0\end{array}\right)$ ．