Then came a technological breakthrough in the United State, where firms found a way to free gas previously trapped in shale rocks.

后来，美国在技术上有了新突破，一些公司发现了从岩石中提取天然气的方法。

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Then came a technological breakthrough in the United States, where firms found a way to free gas previously trapped in shale rocks.

后来美国出现了技术突破，一些公司发现了从页岩中提取天然气的方法。

youdao