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约好下周末去北京旅游，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 , informed 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