假如你是李华，国际学校的教师Paul邀请你星期六参加该校举行的“中国文化日”活动。但你爷爷突然生病住院，你要和父母一起去医院探视，不得不谢绝他的邀请。请根据下列要点用英语给Paul写一封电子邮件。
要点：1.谢绝邀请；
2．说明理由；
3．预祝活动成功。
注意：1.词数100左右；
2．可以适当增加细节，以使行文连贯；
3．邮件开头和结尾已为你写好。
Dear Paul，
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Yours，
Li Hua
Dear Paul，
Thank you very much for inviting me to attend the “Chinese Culture Day” to be held at your school this Saturday. I have been looking forward to it. I believe it will give your students more ideas about Chinese culture and will be great fun. However，much to my regret，I shall not be able to make it now. My grandpa suddenly fell ill and is in hospital. I will visit him with my par
ents on Saturday.
I’m awfully sorry for the sudden change of plan and feel it a great pity to miss the opportunity to be with your students. I wish the activity a great success and hope I will have another chance to join you in the future.