Dear Tina：
I am grateful to you to invite me to your birthday party, I also want to, but recently my body is not too uncomfortable, so I can not come, but Happy birthday to you! I hope you can forgive me!
Yours Kerry
（很感谢你能请我参加你的生日派对,我也十分想来,但是最近我的身体有点不太舒服,所以没法过来,但是仍然祝你生日快乐!希望你能原谅!）