题目内容：

短文改错

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l0处，多者(从第11处起)不计分。

Though a great progress has been made in science these years ,there are still many people live in poor conditions .They make their living by collecting and selling used thing .Their children cannot go to school because they had not enough money to send their children here .Why you think so many people still suffer from poverty now?The answer lies on the population explosion.A president of a developing country once said ,“It is us who are to blame for the poverty because we used to producing children without limit .”Although these few words sound simple enough ,they have clear pointed out one of the causes of the population explosion.