[解析]
Dear Mr.Smith,
How is it going?I'm back home in China now.And I would like to express my most sincere thanks for your kindness to allow me to stay in your home during my visit to California.(高分句型一)Today I'm writing to ask you for a favor.
It seems that I have left behind an English dictionary at your house.It is given to me as a gift by my American teacher.It is such a thoughtful gift that I can't bear losing it.I imagine that it might have been left on the bookshelf in the bedroom I stayed in.(高分句型二)If it is found,could I trouble you to send it back to me please?Of course,the postage will be at my expense.
Thank you again and I hope to see you soon.
Yours,
Li Hua