Dear Tom,
Thanks for your invitation.I really want to come but I'm not available.First,my parents are out on business.And my grandmother had the flu.So I have to look after her.Second,according to my headmaster's calendar,there will be a big this month.I have to prepare for it.
Although I can't come to your birthday party,I can help you something like thinking of the games to play.I really hope you will have a good time.
Happy birthday!
Yours,
Li ping
