Dear Prof. Wu,
I'm your student Li Ming. Now I'm trying to get admitted by the graduate school of Harvard University. As the program asks us to submit a recommendation letter, I'm wondering if you could have the time to write something about my learning experience here in this university. I like your teaching methods. I got interested in what you've taught us and now I'm getting good at it, too.
I know there is a lot of trouble, but I would really appreciate your help if you could kindly agree.
Best regards,
Li Ming