假设你是新华中学的学生李华，你和在上海上学的英国朋友tom约好下*去北京旅游，但你因故不能赴约。请根据以下要点用英语给他写一封电子邮件：
1. 表示歉意; 2. 解释原因; 3. 另约时间。
【参考范文】
dear tom,
i am indeed very sorry that i can't go to beijing with you next week , which i have promised .i feel sorry for about it and want you to know what happened .
just now ,my cousin , li qiong , who left home to australia for his further study last year , *rmed me that he would return this saturday morning and asked me to pick him up at the airport with his family . you know , we haven't seen each other for nearly a year .
i sincerely hope you can accept my apologies and understand me . i would appreciate your allowing me to make another date to show you around beijing .once again ,i'm sorry for any inconvenience caused .
sincerely yours,
li hua
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