In this aerial photo taken on Feb. 21, 2019, staff members from Guiyang high-speed railway maintenance division deal with dilapidated stones over a tunnel for Shanghai-Kunming high-speed train in southwest China's Guizhou Province. The division's main task is to check and repair the facilities on the railway for high-speed trains threading through Guizhou Province where karst landform poses a threat to the security to the passing trains. (Xinhua/Liu Xu)