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。

    I'm Li Hua , a student from FenDou Middle School, that has a history of 75 years. Lie in the west of ShanBa, it has seen great changes of this old town. I am proud to tell you that I studied hard since I came here. So far, under the help of my teachers and classmates I have learned lots of knowledges. Although I still have some trouble with maths at present, I won't lose my heart. I consider it not very difficulty to learn it well as long as I devote myself to learn it. I strong believe that I can be admitted by a key university.

作文：

       题目：以“我学会了                     ”为题写一篇文章。

       要求：①补全题目；②立意自定；③文体自选；④不少于600字；⑤文中不得出现真实姓名、校名等。

1929—1933年，资本主义世界发生了一空前严重的经济危机，使美国的经济政策由胡佛的自由放任转变为罗斯福的国家干预。你认为这一变化的实质是（    ）