改错题

Dear Editor,

    I am writing tell you about the discussion we've had about whether it is necessary of middle school students to have mobile phones. Most students think this is more convenient for them to keep in the touch with their parents and classmates. And what's much, it's a fashion. However, most teachers think middle school students are not old enough to control them. It is a waste of time for students to play games and sending messages on their mobile phones. Therefore, it is easy to make students contact with each other. In my opinion, following the fashion was understandable. But as middle school student, we should put all our energy into our study.

Yours truly,

Mary

在1×2×3×4×5×…×99×100的积中，从右边数第20个数字是____ ．

矩阵$A=\left(\begin{array}{cc}1& 0\\ 0& 2\end{array}\right)$，向量$\overrightarrow{\alpha }=\left(\begin{array}{c}1\\ 2\end{array}\right)$，则$A^{10}\overrightarrow{\alpha }$= （ 　　）