材料一：三湘都市报2014年11月12日报道：因提醒同学值日打扫发生纠纷，在长沙一中专学校就读的16岁女生小梦连续两天被班上15名女同学在宿舍围殴，导致鼓膜穿孔、肾挫伤，并被拍裸照威胁。打人者包括班长、副班长、纪律委员等朝夕相处的同学。小梦被打时当时宿舍里共有6名室友，其中5人看着她被打了3个小时，既没劝架也没报告老师，1人还参与了群殴。小梦说，“虽然我知道那些沉默的室友是害怕被报复没劝架．但我心里没法原谅她们的冷漠。”

材料二：齐鲁晚报2014年12月18日报道：近日，沂源县历山街道新城路小学采取多举措防止校园暴力。一是召开全体师生会议，普及防暴力常识；二是加强门卫管理，控制外来人员进入；三是各班通过班班通观看模拟制伏“歹徒”持刀袭击校园学生的场景，让师生明白该如何应对校园暴力。此举提高了全体师生应对突发暴力事件的能力。

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：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。

    There was a time when my sister was very sad. She used to be a happy girl but was one of the top student in her class. But she lost her left leg in an accident when she is in high school. She was taken hospital and stayed for a long time. Feel very sad, she shut her in her room and refused to communicate with others. All of us were worried about her. One day she learned about a girl whom didn't lose heart though she lost her leg in an earthquake. My sister was deep moved. She had decided to forget the terrible experience and face her life bravely. Now she is living the happy life.

已知a=$\sqrt{2}$，b=$\sqrt{5}$，用a、b的代数式表示$\sqrt{20}$，这个代数式是（　　）

已知α，β是两个不同的平面，a，b是两条不同直线，给出条件：①α∩β=∅；②a⊥α，a⊥β；③a∥α，b∥α，b⊂β．上述条件中能推出平面α∥平面β的是____ ．（填写序号）．