Visitors view a 3D printing machine at China Building Science Conference and Green Intelligent Building Expo in the national convention and exhibition center in Tianjin, north China, June 24, 2021. Tianjin holds the first Green Intelligent Building Expo from June 24 to 27, with a focus on new materials, latest technologies, new equipment, and new energy in the building industry. (Xinhua/Zhao Zishuo)
