题目

I saw________Tom________Jack. There was nobody in the classroom at all. A . either, or B . not, but C . not only, but also D . neither, nor 答案：D13．已知|$\overrightarrow{a}$|=3，|$\overrightarrow{b}$|=4，＜$\overrightarrow{a}$，$\overrightarrow{b}$＞=60°，求（$\overrightarrow{a}$+2$\overrightarrow{b}$）•（$\overrightarrow{a}$-3$\overrightarrow{b}$）=-93．