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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Because of the longer repair time for underground transmission systems, expensive duplication facilities are sometimes installed to reduce the risk of overlap-ping outages4.

由于地下输电系统的修理时间较长，因此有时就安装双套重复设施以降低重叠停电的危险。

youdao

Because of the longer repair time for underground transmission systems, expensive duplication facilities are sometimes installed to reduce the risk of overlap-ping outages4.

由于地下输电系统的修理时间较长，因此有时就安装双套重复设施以降低重叠停电的危险。

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