Citizens board and get off a train of Jinan Subway Line 4, in Jinan, east China's Shandong Province, Dec. 27, 2025. China's first subway line passing through a karst spring area began operation on Saturday in Jinan, marking an engineering breakthrough that balances urban transit demands with the protection of natural water resources. Jinan Subway Line 8 and the east section of Jinan Subway Line 6 started operation on the same day, increasing the city's total rail transit mileage to 248 kilometers. (Xinhua/Zhu Zheng)