Thank you for your email! I feel really honored for your offer from XXX. But after careful consideration, I'm afraid I could not attend your university. It is a decision made by me and my family.
At the same time, I recommend XXX, who is also applying your program, for this offer. He has a strong background and, I believe, also deserve it. Please kindly review his application.
If there is anything I have to do regarding my decline, please let me know.
Your offer letter has been carefully reviewed. I regret to inform you that my girlfriend is not able to recommend my matriculation to your college. Due to the large number of schools that offer me admission and financial support, and the only limited opportunity that I can give, many schools that are very competitive are declined. All this is to say that I have to turn away more schools than I would like in my effort to achieve sound matches between my strengths and that of the departments.
Please accept my best wishes for success in your department development.