I’m writing to…是一个可以用于多种书信类英语作文的首句，用法举例：
1. 告知
① I am writing to inform you of the details of the activity to be held next week at our school.
② I am writing to inform you that an activity is to be organized for foreign students next Monday in our school.
2. 道歉：
③ I am writing to apologize to you for my not being able to accompany you to Beijing.
3. 咨询：
④ I am writing to inquire about your advertisement in ‘The Times’.
⑤ I am writing to inquire whether you need a typewriter.
4. 邀请：
