【正确答案】Dear Prof.Smith,
　　I am sorry to tell you that I have to cancel my travel plan to your city for some reasons,thus I am afraid that I couldn't visit you according to the due cource.So I am writing for the purpose of extending my sincere apology to you.
　　Actually, I miss you very much, but I received a notice suddenly that I have to attend an exam if I would love to apply for an opportunity for further study abroad.Nevertheless I haven't prepared for it very well Hence I have to spend more time and energy on it.
　　Please accpet my hearfelt apology again! I am really sorry for any inconvenience I caused. And I am honorable to ask if I could make an another appointment with you.I am looking forward to your response at your earliest convenience. Regards !
　　Yours faithfully,
　　Li Minge Part B