1. I am writing to express my heartfelt（真诚的） gratitude for your help before the final exams.
我写这封信为了表达对你衷心的感谢，因为期末考试前你帮助了我。
2. My gratitude to you is beyond words.
我对你的感激无以言表。
3. I am fortunate enough to have you as my best friend.
我很荣幸能够拥有你这个最好的朋友。
4. It is really a big favor you have done me.
你帮了我大忙了。