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处错误，每句中最多有两处。错误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(Λ)，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。
Some day I happened to find a chatting room in my QQ, there people were chatting in English. I tried to chat with some of them. To my surprised, I found the oral English of some junior students were better than me. I asked them for advice and they told me to practise more on QQ. But every day after that I would spend one hour practise my oral English on QQ. Day by day I learned from many useful words and expressions. With time go by, I found that I could even communicate some college students freely.
，用定义证明：F（x）在R上为单调递减函数．
