增加：在缺词处加一个漏字符号（∧），并在其右边横线处写出该加的词。

删除：把多余的词用斜线（﹨）划掉，在该行右边横线写出该词，并用斜线划掉。

修改：在错的词下划一横线（__），并在该行右边横线写出修改后的词。

    Nowadays big cities may be wonderful places to live. There are many nice things to see and to do. And there are serious problems in big cities. The cost of living is high.

    Every year many people move to the cities because of more chances (机会)to find job or good schools. But sometimes some people can't. Also, having too many people in a small place makes it hard to keep the cities safe and clean. Someone enjoy staying in big cities, but others don't. There really are a lot of problems, so you should think about it carefully before moving there.