Dear Anne,
Thank you for your invitation to dinner at your home tomorrow evening. Unfortunately, it is much to my regret that I cannot join you and your family, because I will be fully occupied then for an important exam coming the day after tomorrow.
I feel terribly sorry for missing the chance of such a happy get-together, and I hope that all of you enjoy a good time. Is it possible for you and me to have a private meeting afterward?
If so, please don’t hesitate to drop me a line about your preferable date. I do long for a pleasant chat with you.
Please allow me to say sorry again.
Faithfully yours,
Li Ming