【正确答案】Dear Carlos,
I am back in London now. 1 just write to thank you for your hospitality and the honor you showed to me during last week. I will always remember this wonderful visit. It was so nice of you to arrange so many interesting things especially the visits to the Great Wall, the Imperial Palace and the Summer Palace, which would be unforgettable for the rest of my life. Also I will never forget those kind friends you have introduced to me.
I hope you will pay a visit to London someday and give me a chance to reciprocate your kindness.
With my sincere thanks for your kindness!