过去没有完成的事情

Dear　　,
　　I am writing this letter to apologize to you for my failing to _____.
　　The reason is that ______. I am sorry that I cannot finish in time, but is it possible that I make up the loss by offering you ______? If so, I will put everything else aside to _____.
　　I do hope that you can understand my situation and accept.

　　将来不能做的事情

Dear _____,
　　I am terribly sorry that I am unable to _____ . It is mainly because at that time I will be fully occupied by _____ which is quite out of my expectation, and that conflicts with your ______ . 　　　　　　　　　　　　　Therefore I am forced to adjust my schedule and cannot make my presence on your ______.
　　I sincerely hope that you will enjoy a good time. By the way, can we have dinner together/ make another appointment some time next week? I hope to see you soon.
　　Once again, I am sorry for any inconvenience caused. I hope that you will understand my situation.