下面短文中有10 处语言错误。请在有错误的地方增加、删除或修改某个单词。
增加：在缺词处加一个漏符号（∧），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，并在该下面写出修改后的词。
注意：
1. 每句不超过两个错误；
2. 每处错误及其修改均仅限一词；
3. 只允许修改10 处，多者（从第11 处起）不计分。
Several days ago, our school decided to prevent students bringing their cell phones to school if they don’t pass all exams from the previously semester. Students don’t welcome this decision.They believe the cell phone is one of the greatest invention in the 20th century, that have become an important part of modern life. Therefore it is also headache for school leaders. Because many students ignore our studies and spend too much time play games, texting and using social network apps such as Wenxin or Wechat. So the leaders have to deal with the serious problem by this way.They don’t expect that something even worse.