根据提示写一封60~80字的信。

Tom 邀请Li Ping 参加他这周日的生日宴会，但Li Ping的父母出差要到下个月回来，奶奶又卧病在床，需要人照顾。再说英语考试即将来临，因此，无法前去参加生日宴会。Li Ping感到很抱歉，只好写信辞谢。

Dear Tom,

Thank you very much for inviting me to your birthday party.I'd love to go but I can't.

My parent____________________________________. From Li Ping

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 English 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.