星期四下午,两节数学课。上课铃还没打,许老师就大步流星地走了进来,班里一下子安静下来。许老师取下挂在窗把手上的那把有些年头的大三角尺,接着,黑板与粉笔接触的“哒哒”声和绘制直线流畅的“刷刷”声汇成了教室里的主旋律。他很严厉,但却被我们敬爱着。听说许老师教的数学是我们学校的“王牌”。“这道题考的是旋转。”许老师指着那个三角形说,“所以我们......”他忽然打开了讲台里的大抽屉,取出了一张之前剩余的考卷。 Thursday afternoon, two math classes. The bell did not hit the bell, Xu teacher went on a stride came, the class suddenly quiet. Xu took off the old triangular ruler hanging on the window handle and then came into the classroom with the “da da” sound in blackboard and chalk and the straight brush “sound” The main theme. He is very harsh, but he is loved by us. I heard Professor Xu taught mathematics is our school “ace ”. “This exam is a rotation. ” Xu pointing to the triangle said, “So we ... ” He suddenly opened the podium in the big drawer, took out the remaining papers before .