短文改错（共10小题；每小题1分, 满分10分）

　假定英语课上老师要求同桌之间交换修改作文，请你修改你同学写的以下作文。文中共有10处语言错误，每句中最多有两处。错误涉及一个单词的增加、删除或修改。

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；

Air travel has three advantage over train travel. First, it can save much time. We can fly from one place to other in a long time, but by train we have to spend more time. Second, air travel is more comfortable because the plane flies so smooth that we can have a good rest during the trip. Third, the train is crowding sometimes and passengers have to sit for a long time, what makes them tired. But train travel also has it’s own advantages. For an example, traveling by train cost only a little money. Besides this, we can enjoy the view out the train’s windows.

简述“市场失败”的主要内容。