Dear Danny,
I am terribly sorry to tell you that l am unable to keep my promise to attend your birthday party tomorrow evening.That is owing to the fact that my younger brother suddenly fell ill and was taken to the hospital this morning.I have to go there immediately and care for him.As told by the doctor in charge,it will take around five days for him to recover and l have asked my boss for a week's leave.
I really regret that I cannot go to celebrate your birthday personally and would miss the perfect chance of enjoying myself with all our old friends.I have chosen a **all gift for you and will send it to you tomorrow to show my best wishes.Besides,please give my regards to our friends when you meet them at the party.
Cordially,
Ben
参考译文：
亲爱的丹尼:
我很遗憾地告诉你，我无法兑现明天晚上参加你的生日聚会的承诺了，因为我的弟弟突然生病，今天早上被送往医院。我必须立即去那里照顾他。 根据主治医生的说法，他需要大约五天的时间来恢复，我巳经向我的老板请求休假一周。
我真的很遗憾不能亲自去庆祝你的生日，并错过与我们所有的老朋友享受快乐时光的完美机会。我为你选择了一个小礼物，明天寄给你，以表示我最美好的祝愿。 此外，当你在聚会上见到我们的朋友时，请帮我问候们。
诚恳的，
本