在整数集Z中，被5除所得余数为k的所有整数组成一个“类”，记为k，则k=5n+k，k=0、1、2、3、4，则下列结论正确的是 ____

①2013∈3

②Z=0∪1∪2∪3∪4

③“整数a、b属于同一‘类’”的充要条件是“a﹣b∈0”

④命题“整数a、b满足a∈1，b∈3，则a+b∈4”的原命题与逆命题都为真命题．

增加：在缺词处加一个漏字符号（∧），并在此符号下面写出该加的词。

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。

    Last Saturday I went to the Great Wall with some of my friends.In our way up,we saw many volunteers working in the sun.They helped the elders with their bags,took photo for some tourists and answered people's questions.Because they were very tired,they didn't stop to have a rest.Just at the moment,we saw a little boy standing alone,cried.We went over and asked what is the matter.From his answer we knew he couldn't find her mother.We told him not to worry and then we tried to get in the touch with his mother with the phone number he had given us. Twenty minutes late,his mother turned up,and thanked us again and again.That day we enjoyed the beauty of the Great Wall,and felt the warm of the society.If everyone can reach out helping to others,the world will be more harmonious.

街心公园的总面积为24000平方米，其中建筑、道路等占公园总面积的25%，其余为绿地．街心公园的绿地面积有多少平方米？