如果把绿叶比作“绿色工厂”，那么其动力是（ ）

增加：在缺词处加一个漏字符号（ ）,并在其下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1). 每处错误及其修改均仅限一词；

2). 只允许修改10处，多者（从第11处起）不计分。

    When I was a child, I spent more than ten years learn the violin．Therefore, I couldn't understand "real music"．After I graduated at high school, a friend of mine suggested that we started to learn the guitar because we all thought it was cool．l will never forget the day on that we went to buy guitars in the guitar store．There I saw a guitar player playing the guitar, which I really enjoyed．He became my the first guitar teacher．It took me such a long time choose a guitar among several wonderful model．Now the guitar is the most importantly part of my life and I practise it every day.

63÷21=____

98÷49=____

50×20=____

51÷17=____