Dear Mr. Black,

I am really sorry about my using the mobile phone in your lecture yesterday. Please accept my heart-felt apology for being so rude a student.

I know any word might sound a make-up excuse. But I didn’t use my mobile phone for no reason. I was trying to (….学生当时使用手机的理由….) Therefore, I got no choice but try sending them a text message in class and that was exactly what I was doing when you discovered.

Anyway, using a mobile phone in a classroom was not acceptable to any teacher. I make sure it will not happen again. But I do need my phone back to keep in touch with others.

Will you be so kind as to give it back to me. Thanks a lot!

Best wishes!

Yours sincerely

Liu Ming

题目分析：题目要求写一封道歉信，向外教道歉。写作要点包括：表达歉意；解释使用手机的原因；提出请求并作出保证。使用第一人称进行写作，注意书信的格式和礼貌用语；书写工整，不要出现标点和拼写错误，正确使用时态和语法知识。

【亮点说明】范文使用了非谓语动词my using the mobile phone，being so rude a student，using a mobile phone；

固定句型：got no choice but try sending them a text message；表语从句what I was doing；宾语从句make sure it will not happen again等语法知识，显示了一定的语法基础；

范文还使用了一些固定短语：keep in touch with；so kind as；give it back to等，使作文内容变得充实；

范文注意使用But，Therefore，Anyway等衔接前后句和上下文，是作文显得紧凑，前后联系紧密。