包括地下蒸汽储藏的地热能，也是无污染的。
Geothermal energy, which involves stored underground reservoirs of steam, is also pollution-free.
努力寻找赞助商以帮助全面恢复整个斗兽场，包括地下部分的更多的区域的工作，正在进行之中。
Efforts to find sponsors to help fully restore the entire Colosseum, including more of the underground section, are underway.
即便是所谓的“清洁煤”(包括地下碳汇)堪用，该项技术已被延误多次，仍然未经证实，况且至少还需要15年的时间。
So-called "clean coal" -including underground carbon sequestration-could work, but the technology has repeatedly stalled, remains unproven, and is at least 15 years away.
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