Dear Professor Xu,
I am writing to extend my gratitude to you. Because of your help，now I am a student of Chemistry Department of University of California.
Last April, when I applied to become a graduate student of University of California, you really gave me a lot of valuable help. You not only wrote a recommendation for me to Professor Wells who works in the University of California，but also gave me careful and patient instructions on how to fill the application forms and write the application letters.
It is your unreserved help that enables me to obtain this splendid opportunity of further education. For the following two years I will study hard to reciprocate your sincere help and expectations with excellent grades.