Which cities in China have subway systems?

在中国有哪几个城市有地铁？

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The complexity of subway systems around the world is mind-boggling.

全世界地铁系统错综复杂，令人眼花缭乱。

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The effective design and functional operation of fire safety measures in subway systems are discussed.

另外，还讨论了地铁系统的有效设计和火灾安全设施的正常运作情况。

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Subway systems from Shanghai and Dubai to Paris have installed safety doors over the last three decades.

WSJ: NYC subway safety options discussed

There has been a push in recent years to combat this by putting recycling bins (instead of trashcans), in the subway systems.

FORBES: Recycling Fiber (Paper)...The Basics...

Sewers can contain dangerous gases, subway systems can have unpredictable train schedules, abandoned buildings can be crumbling or have asbestos, and usually it is illegal to access the sites.

BBC: Discovering an unseen urban underworld