12.删除:把多余的词用斜线(\)划掉.
增加:在缺词处加一个漏字符号(∧),并在其下面写出该加的词.
修改:在错的词下划-横线,并在该词下面写出改正后的词.
Thanks for your letter.I've thought a lot of about whether you should buy a laptop computer help you with your study.In my opinion,you'd better not.For one reason,it's very easy for you to develop some habit.Once you have it,such as playing computer games,see movies and so on,which will be a waste of time.For other reason,buying a laptop computer don't mean you can study well.If you want to make a progress,you need to put your heart into your study but work hard.Whether you had a computer or not is not the most important.Do you agree to me?Looking forward to your early reply!