Put those shuttle routes underground with the maglevs, and save the runway slots for the routes where you can’t justify building expensive tunnels.

把那些穿梭航线与地下的磁悬浮链接，并在那些你必须建立昂贵隧道的地方留下地铁的槽。

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One possibility — a process that would inject carbon dioxide deep underground for storage — is a largely untested technology that is likely to be very expensive.

一种可能是将二氧化碳深埋于地下，不过这种技术很大程度上还没有经过检验、而且可能造价昂贵。

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They believe dumping carbon underground is expensive and risky for local environments.

他们知道往地下倾倒二氧化碳非常昂贵，并承担着破坏当地环境的风险。

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The problem: The city insisted that the buyers first build a hugely expensive underground parking garage and seawall.

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The coal is deep underground and expensive to extract.

ECONOMIST: What is good news for miners is bad news for the environment

But going underground is an expensive proposition: The direct costs are much more than those associated with traditional overhead power lines.

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