矩阵 $\boldsymbol{A}=\left(\begin{array}{cc}1 & -1 \\ -1 & 1\end{array}\right)$, 与 $\boldsymbol{A}$ 合同但不相似的矩阵为
A. $\left(\begin{array}{ll}1 & 1 \\ 1 & 1\end{array}\right)$.
B. $\left(\begin{array}{ll}2 & 0 \\ 0 & 0\end{array}\right)$.
C. $\left(\begin{array}{ll}3 & 0 \\ 0 & 0\end{array}\right)$.
D. $\left(\begin{array}{ll}-1 & -1 \\ -1 & -1\end{array}\right)$.