Guo Zhiyun from School of Life and Science at Southwest Jiaotong University gives a lecture about tumour during a science popularization activity in Chengdu, southwest China's Sichuan Province, Sept. 18, 2018. Around 18,000 science promotion activities will be held nationwide during the National Science Day which lasts from Sept. 15 to 21. (Xinhua/Jiang Hongjing)