百度 城市河道污染的主要来源包括河道水面与上游的污染物、径流污染、生产生活用水污染等，要想使这些污染被控制，可以修建排水管网和污水处理厂，从而使河道污染得到有效控制。
By Ren Xu, Zhang Dongpan, Liu Dan and Guo Xiaoning
BEIJING, May 23 -- The first batch of Chinese troops participating in the China-Mongolia "Steppe Partner-2024" joint army training departed Mongolia for home on the afternoon of May 21.
Before departure, the Mongolian side held a brief farewell ceremony at the train station according to traditional etiquette.
The Steppe Partner-2024 this year marks the first joint exercise between Chinese and Mongolian armies. The Chinese participating troops began withdrawal on May 21 in succession. According to the plan, nearly 100 vehicles will be transported by train in three echelons, which is expected to be completed by May 24.
