如何委婉拒绝他人生日聚会邀请

　　Dear Lisa：

　　Thanks for your invitation.I'd love to your birthday party,But I can't.My mother had a flu,I must look after her,And I also have a cold these days.Because of these,I have a lot of homework don't finish.And I must prepare for the exam.So i'm very sorry I can't come.Let me see happy birthday to you now.Wish you have a good time!

　　Yours Tom