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。

    I am used to be a naughty boy, who always made my parents annoyed from time to time. One day, as I was wandering around the field near my house, a cricket attracts my attention and I couldn't help catch it. I was noticed doing all this by Nick, a friend of mine, and he said to me, “Let's put the cricket on Selina's desk to frighten her, all right?”Of course I said yes, and I, together with him, were going to do just as what we had discussed. A few minutes before our trick, Selina saw it and was so frightened that she fell off the chair and broke his head, Afterwards, criticizing by my parents, I was made apologize to her. This lesson taught me a lot, warning me not to play a trick at other people. Since then, I have done things much well than before and become a man with manners and dignity.

先化简，再求值：$\frac{2m+n}{m^2-2mn+n^2}$•（m﹣n），其中$\frac{m}{n}$=2．

查阅资料：

①氨气水溶液呈碱性

②浓硫酸和碱石灰都可做气体吸收剂；浓硫酸能吸收氨气，不能吸收二氧化碳；碱石灰是氧化钙与氢氧化钠固体的混合物，不与氨气反应。