X. One possible version：
May 23th， 20xx
Dear Mr Qiu，
Thank you so much for teaching me so well. You are very kind to me. During the last three years I have learnt a lot of knowledge from you. I’ll never forget you. I’ll keep on studying hard as usual in the senior middle school.
Wish you success in the future teaching work. Wish you a healthy body for ever. And wish you a happy life in the future. And I also hope that everything will go well in our school！ Best wishes for you and for our school！
Your student，
Li Hong