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10处，多者（从第11处起）不计分。

    Everyone should take the action to reduce haze (雾霾), which is harmless to our health. First of all, I believe that if we plant more tree, there will be less haze in their city. Trees can absorb exhaust fumes (尾气) from cars, thus reduce pollution. Second, the government should punish the factories where produce too many fumes. Exhaust fumes is the main cause of haze and do greatly harm to people's health. Maybe we can move factories to areas where few people live. Third, I think it was a great idea to encourage people to use public transportation. Last but not least, we can call on citizens ride bikes if they travel short journeys.

已知点A（1，1），B（3，3），则线段AB的垂直平分线的方程是（　　）