Dear Trong L, Thanks for sharing your all-sided feelings about the long trip in Tibet and Xian. And most of all we feel grateful to know that you are pleased with all the guide, driver, hotel and meals in both two places. According to your feedback about Lhasa, I see you may go through an altitude sickness that is indeed a bit exhausting. But even though you still got over it and had a memorable travel experience. Thanks for your considerate notice about oxygen matters, I think it will be greatly helpful to others who plan to visit Tibet or other places with high altitude. Generally, we sincerely hope to meet you again in china if there's more chances. All my best wishes, Sophia