Photo taken on Dec. 15, 2004 shows the construction site of the Qinghai-Tibet Railway. (Xinhua/Chogo)

A cargo train runs on the prairie in north of southwest China's Tibet Autonomous Region, June 10, 2019. (Xinhua/Chogo)

Photo taken on March 23, 2004 shows the first locomotive in southwest China's Tibet Autonomous Region. (Xinhua/Chogo)

A cargo train runs on the prairie in north of southwest China's Tibet Autonomous Region, June 10, 2019. (Xinhua/Chogo)

Photo taken on Oct. 9, 2004 shows the construction site of the Qinghai-Tibet Railway. (Xinhua/Chogo)

An ethnic Tibetan talks with a staff worker of the Qinghai-Tibet Railway on June 20, 2004. (Xinhua/Chogo)