Photo taken on Dec. 1, 2019 shows the construction site of a bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)

Workers of China Railway 11 Bureau Group Co., Ltd. prepare to lay steel rail for a bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region, Dec. 1, 2019. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)

Photo taken on Dec. 1, 2019 shows the construction site of a bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)

Photo taken on Dec. 1, 2019 shows the construction site of a bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)

Photo taken on Dec. 1, 2019 shows a bridge above the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)

Photo taken on Dec. 1, 2019 shows the construction site of a bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)

Workers of China Railway 11 Bureau Group Co., Ltd. lay steel rail for a bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region, Dec. 1, 2019. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)

Workers of China Railway 11 Bureau Group Co., Ltd. lay steel rail for a bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region, Dec. 1, 2019. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)

Workers of China Railway 11 Bureau Group Co., Ltd. lay steel rail for a bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region, Dec. 1, 2019. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)

Workers of China Railway 11 Bureau Group Co., Ltd. lay steel rail for a bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region, Dec. 1, 2019. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)

Workers of China Railway 11 Bureau Group Co., Ltd. lay steel rail for a bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway in Sangri County of Shannan, southwest China's Tibet Autonomous Region, Dec. 1, 2019. The rail-laying work of a 4,615-meter-long bridge crossing the Yarlung Zangbo River of Lhasa-Nyingchi railway was completed on Sunday. The Lhasa-Nyingchi railway features complex geological conditions, with a total length of 435 km, 75 percent of which are bridges and tunnels. The construction work began in 2015 and is expected to be completed in 2021. (Xinhua/Chogo)