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. $\left[\begin{array}{ll}-1 & -1 \\ -1 & -1\end{array}\right]$.