【答案解析】Dear Li Xu,
Thank you for helping me study physics for the final exam. Since I was sick for a long time, I wasn"t sure if I"d be able to catch up on all the lessons. However, I ended up with an A in the test, which is much better than what I expected. I would not have had such a good grade if you hadn"t helped me review.
Thanks for setting aside the time to help me. I want to let you know that your thoughtfulness did not go unnoticed. I really appreciate your help, and I want to assure you that I am more than willing to help you in the future.
Once again, I would like to take this opportunity to express my great appreciation for your timely help and assistance.