Dear ,
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 dont 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.
Regards,
Li x
翻译：
亲爱的x：
感谢您邀请我于明日晚上与您和您的家人共进午餐。可是，我非常遗憾地告诉您我无法赴约，因为我将忙于准备后天的一门重要考试。错过了这么一个欢乐的聚会我深感遗憾，我希望您们能度过一个愉快的时光。对了，在我考试后我们可以见一面么?如果可以的话请给我打电话，我非常期待能和您愉快地聊天。
请允许我再一次致歉。
您真诚的，
李x