Dear Tom, Thank you very much for inviting me to your birthday party. I'd love to go but I can't. My parents are out on business. They are coming back next month. And now I have to look after my grandma because she is ill in bed. And I also need to study for my coming math exam. I'm very sorry but I can't go to your party. Thank you for asking me. I hope you can have a good time. From Wei Hong