Workers lay tracks on the Yarlung Zangbo River bridge of the Lhasa-Nyingchi section of the Sichuan-Tibet Railway in Gonggar County of southwest China's Tibet Autonomous Region, Nov. 26, 2018. The Yarlung Zangbo River bridge, the first cross-river bridge on the Lhasa-Nyingchi section of the Sichuan-Tibet Railway, started its track laying on Monday. (Xinhua/Purbu Zhaxi)

Workers lay tracks on the Yarlung Zangbo River bridge of the Lhasa-Nyingchi section of the Sichuan-Tibet Railway in Gonggar County of southwest China's Tibet Autonomous Region, Nov. 26, 2018. The Yarlung Zangbo River bridge, the first cross-river bridge on the Lhasa-Nyingchi section of the Sichuan-Tibet Railway, started its track laying on Monday. (Xinhua/Purbu Zhaxi)

Workers lay tracks on the Yarlung Zangbo River bridge of the Lhasa-Nyingchi section of the Sichuan-Tibet Railway in Gonggar County of southwest China's Tibet Autonomous Region, Nov. 26, 2018. The Yarlung Zangbo River bridge, the first cross-river bridge on the Lhasa-Nyingchi section of the Sichuan-Tibet Railway, started its track laying on Monday. (Xinhua/Purbu Zhaxi)

A worker lays tracks on the Yarlung Zangbo River bridge of the Lhasa-Nyingchi section of the Sichuan-Tibet Railway in Gonggar County of southwest China's Tibet Autonomous Region, Nov. 26, 2018. The Yarlung Zangbo River bridge, the first cross-river bridge on the Lhasa-Nyingchi section of the Sichuan-Tibet Railway, started its track laying on Monday. (Xinhua/Chogo)

Photo taken on Nov. 26, 2018 shows the construction site of the Yarlung Zangbo River bridge of the Lhasa-Nyingchi section of the Sichuan-Tibet Railway in Gonggar County of southwest China's Tibet Autonomous Region. The Yarlung Zangbo River bridge, the first cross-river bridge on the Lhasa-Nyingchi section of the Sichuan-Tibet Railway, started its track laying on Monday. (Xinhua/Chogo)

Workers lay tracks on the Yarlung Zangbo River bridge of the Lhasa-Nyingchi section of the Sichuan-Tibet Railway in Gonggar County of southwest China's Tibet Autonomous Region, Nov. 26, 2018. The Yarlung Zangbo River bridge, the first cross-river bridge on the Lhasa-Nyingchi section of the Sichuan-Tibet Railway, started its track laying on Monday. (Xinhua/Purbu Zhaxi)

A worker is seen at the construction site of the Yarlung Zangbo River bridge of the Lhasa-Nyingchi section of the Sichuan-Tibet Railway in Gonggar County of southwest China's Tibet Autonomous Region, Nov. 26, 2018. The Yarlung Zangbo River bridge, the first cross-river bridge on the Lhasa-Nyingchi section of the Sichuan-Tibet Railway, started its track laying on Monday. (Xinhua/Purbu Zhaxi)

Workers lay tracks on the Yarlung Zangbo River bridge of the Lhasa-Nyingchi section of the Sichuan-Tibet Railway in Gonggar County of southwest China's Tibet Autonomous Region, Nov. 26, 2018. The Yarlung Zangbo River bridge, the first cross-river bridge on the Lhasa-Nyingchi section of the Sichuan-Tibet Railway, started its track laying on Monday. (Xinhua/Chogo)