A staff introduces the mini-models of drain system of ancient buildings during an exhibition in Qingdao, east China's Shandong Province, July 28, 2019. An exhibition on the mini-models of the ancient buildings in Qingdao is held here in the Qingdao International Sailing Center, during which 60 mini-models are displayed to show the history and culture of the coastal city. (Xinhua/Li Ziheng)