过去的四年里，这株小竹子一直在地下生长，第五年开始，它形成了足够强大的根系，可以在地面生长。

The little bamboo tree had been growing underground for the past four years, in the fifth year and beyond, it developed a root system strong enough for its ground growth.

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他们那痛苦的地下生活持续了超过两个月。

Their subterranean ordeal lasted for more than two months.

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这些水存在的全部区域称为地下生物圈。

The overall region where this water exists is called the subsurface biosphere.

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