I am terribly sorry to tell you that i am unable to attend your birthday part next thursday evening. That is owing to the fact that my younger brother suddenly fell ill and was taken to a hospital this morning. I have to go there immediately and take care of him. as told by the doctor in charge, it will take around five days for him to recover and i have asked my boss for a 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 small 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.
Dear mr. smith,
I am indeed very sorry that i missed the examination on international business english writing you gave last friday. I feel awful about it and want you to know what happened that day.
I suddenly fell sick early that morning and my parents had to send me to the hospital. please find enclosed a copy of the medical bill.
Once again, i apologize for any inconvenience caused.
Dear Professor Martin,
I enjoy your class very much. But I'm very sorry that I had to miss your class last Thursday. Unfortunately my roommate became ill and I had to take him to the hospital. Please let me know what I can do to make up the class. I know you prefer for us to let you know in advance when we will be absent, but there was no time to do so.
I hope you'll accept my sincere apology.