近年来，初中校园欺凌事件时有发生，避免此类事件发生的有效做法有（    ）

①同学间理解和宽容                ②学校对学生进行法制教育

③父母尽到监护责任                ④执法部门公开审理社会施暴者

如图，l₁∥l₂∥l₃，直线a，b与l₁、l₂、l₃分别相交于A、B、C和点D、E、F．若 ，DE=4，则EF的长是（　　）.

增加：在缺词处加一个漏词符号 （^），并在此符号下面写出改加的词。

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。

    My next vacation will be wonderfully for me. I will go to Maryland to visit my friends. I have known her for eleven years since I am in high school. Right now, she is studying English at the University of Maryland. When I visit her, she will have to go to her classes, but we will have lots of free time together either. When we went high school together, she didn't study very much hard. She wasn't getting very good grades. And now she is a very good student in American. She know that she should study hard to success. We will have a great time together this summer.