Dear Zhou Ming
I am sorry for missing your birthday party , but i known the day clearly.i hope you can understand the case is this .Lets me tell you .
Yesterday afternoon a friend of same dormitory were ill suddenly. I saw he can't bear the suffering. So i put aside the work on hand to help him. I sent him to the hospital until 9 o'clock came back school. At the same time. I have not time to go to your birthday party.
I hope you can understand this burst case and forgive me . By the way . Happy birthday to you !
Sincerely
your friend
（我用手机写的,格式有的有点问题,自己可以改正）