Dear Cindy,
Thank you very much for your inventation.But I'm afraid I can't go to your birthday party.
Because i'm very busy.On Monday i will go to see a movie with my parents.I'm going to have a piano lesson on Tuesday.On Wednesday i have to prepare for my exam.On Thursday i must take good care of my grandma at home.I am going to practice tinnes.So,i can't go to your party.
Happy Birthday To you.