有一个孩子发现了一个蝴蝶蛹，看到里面挣扎的蝴蝶，忍不住用剪刀剪开蛹壳，帮助蝴蝶出来。出壳后的蝴蝶由于身躯臃肿，翅膀干枯，不久就死了。

从这个故事中我们得到了什么启示？

假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的以下作文。文中共有10处语言错误，每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。

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。

    Yesterday my English teacher asked each student write a composition title "The Greatest Achievement of My Life". I was not sure how to write about it. I've thought it over for a long time. I do many things. Coming to America, get a job and meeting new people was my achievements. I think my greatest achievement is learning English. Though sometime I don't understand everything people are saying, but each day I get better and better. I told my teacher this was difficult composition to write. Above all, it is hard to measure everything you have done.

若2lg(x-2y)=lgx+lgy，则${\log }_2\frac{x}{y}$的值为（  ）