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若 $\left|\begin{array}{ll}a_{11} & a_{12} \\ a_{21} & a_{22}\end{array}\right|=6$, 则 $\left|\begin{array}{ccc}a_{11} & a_{12} & 0 \\ a_{21} & a_{22} & 0 \\ 0 & -2 & -1\end{array}\right|=$
A. 12     B. -12     C. 18     D. 0         
不再提醒