Dear Tom,

Thanks for your invitation.I really want to come but Im 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 headmasters calendar,there will be a big this month.I have to prepare for it.

Although I cant 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