Journalists visit the command center of Beijing's subway in Beijing, capital of China, Oct. 20, 2017. Chinese and foreign journalists visited the command center of Beijing's subway and subway Yanfang line in Beijing on Friday. (Xinhua/Xing Guangli)

Journalists visit the subway Yanfang line in Beijing, capital of China, Oct. 20, 2017. Chinese and foreign journalists visited the command center of Beijing's subway and subway Yanfang line in Beijing on Friday. (Xinhua/Xing Guangli)

Journalists visit the subway Yanfang line in Beijing, capital of China, Oct. 20, 2017. Chinese and foreign journalists visited the command center of Beijing's subway and subway Yanfang line in Beijing on Friday. (Xinhua/Xing Guangli)

Journalists visit the command center of Beijing's subway in Beijing, capital of China, Oct. 20, 2017. Chinese and foreign journalists visited the command center of Beijing's subway and subway Yanfang line in Beijing on Friday. (Xinhua/Xing Guangli)