A worker checks the condition of the construction of Lanzhou subway line 1 which is 40 meters underground in the Lanzhou section of the Yellow River, capital of Northwest China's Gansu province, May 9, 2016. The construction of the right tunnel of the subway was completed Monday. It's the first subway line to run under the Yellow River. [Photo/Xinhua]

Workers work 40 meters underground in the Lanzhou section of the Yellow River, capital of Northwest China's Gansu province, May 9, 2016. The construction of the right tunnel of Lanzhou subway line 1 was completed Monday. It's the first subway line to run under the Yellow River. [Photo/Xinhua]

Workers check the condition of the construction of Lanzhou subway line 1 which is 40 meters underground in the Lanzhou section of the Yellow River, capital of Northwest China's Gansu province, May 9, 2016. The construction of the right tunnel of the subway was completed Monday. It's the first subway line to run under the Yellow River. [Photo/Xinhua]

Workers work 40 meters underground in the Lanzhou section of the Yellow River, capital of Northwest China's Gansu province, May 9, 2016. The construction of the right tunnel of Lanzhou subway line 1 was completed Monday. It's the first subway line to run under the Yellow River. [Photo/Xinhua]

Workers check the condition of the construction of Lanzhou subway line 1 which is 40 meters underground in the Lanzhou section of the Yellow River, capital of Northwest China's Gansu province, May 9, 2016. The construction of the right tunnel of the subway was completed Monday. It's the first subway line to run under the Yellow River. [Photo/Xinhua]