The quickest way to go round the city is by underground train.

在这个城市四处走动最快的办法就是乘坐地铁。

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The train was trapped underground by a fire.

列车被一场大火困在了地下。

《柯林斯英汉双解大词典》

Consumers will be able to pay for sandwiches, drinks and train tickets by placing their phones close to a reader similar to the Oyster card system on the London Underground.

届时，消费者们购买三明治、饮料和火车票时，只要将他们的手机靠近一个类似应用于伦敦地铁的“牡蛎卡”(Oyster card)系统的读取器，就可以付款。

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Some of the children travelled to performing arts school in London by train and underground during the rush hour, the jury heard.

BBC: Amanda Webber

London Underground is to be prosecuted by the rail regulator over a runaway engineering train.

BBC: Runaway Northern Line Tube train: Charges brought

Take an Underground train a few stops from the borough of Westminster, and life expectancy drops by 12 years.

BBC: Would a new law narrow the gap between rich and poor?