It's the largest subway system in the United States.

这是美国最大的地铁系统。

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As of 2007, it was ranked the fourth-largest subway system in the world.

在2007年，它是世界第四大的地铁系统。

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Shanghai aims to have the world's largest subway system by 2012 and a chunk of the expansion is being inaugurated this month.

上海的目标是到2012年前建成全球最大的地铁系统，一项大型地铁扩建工程将于本月破土动工。

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Also in Japan, Subway, which surpassed McDonald's last month as the world's largest fast food chain, does not just serve fresh ingredients, it grows them in its backyard.

BBC: Would you like fries with that Maharaja Mac?