More than 90 percent of the matter that makes up trees was once water and free-floating atmospheric carbon dioxide.

形成一棵树所需的物质里，90%都来自于水分和空气中的二氧化碳。

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Tractors are tilling the land and building earthen rows that will serve as levees once water flows into these fields.

拖拉机在耕地，并且建起一道道田埂，等水流进这些农田时，这些田埂就能起到河堤的作用。

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It takes just two or three big waves to signal doom: once water flows behind the defences, even the thickest ramparts are swift to collapse.

一两个大浪就可以宣告末日将至：海水一旦流过城墙，再厚的城墙也难逃一塌。

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They walk along the Frijoles stream lined with green trees that once was the only water supply for the valley.

VOA: special.2010.07.05

Pieter Hoff says the nice thing about the siphons is that, once collected, the water is not able to evaporate anymore.

VOA: special.2010.07.13

Huge amounts of water ran into a low area in the dry, waterless desert that had once been an ancient lake.

VOA: special.2009.08.12

Once water is available to the pump, it has to be routed to one or more discharges.

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Native tribes will not have to relocate, but could face a change of lifestyle once water levels shrink.

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Water soaking will loosen them and like a new sponge, once in water it is never the same.

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