A pair of twin girls read books at an air-raid shelter at People's Square in Chongqing, southwest China, July 11, 2018. The air-raid shelters, once used to protect Chongqing residents from air attacks during war time, have turned out to be an ideal place to escape from the scorching heat. Heat waves have hit many parts of the country over the past month. (Xinhua/Wang Quanchao)