Plants keep our air and water clean.

植物能保持空气清新和水源清洁。

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Now, think about what made the water clean.

现在，想想是什么让水变得干净了。

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He swims to teach people about the importance of keeping water clean.

他游泳是为了教导人们保持水清洁的重要性。

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"The sea grass is very important." "It filters the water, it keeps the water clean.

VOA: standard.2010.07.05

The government could also use violations of other federal laws such as the Clean Water Act to collect money for the spill.

VOA: special.2010.06.04

They hope that future synthetic cells can make useful bacteria for products like bio-fuels or vaccines, and to clean up polluted water.

VOA: special.2010.07.20

The region has the highest water bills in the UK, partly because of the cost of keeping the coastal region's sea water clean.

BBC: Water customers have not been given a rebate since 1998

Their plan says that somehow if we eliminate regulations that keep our air and water clean for our kids, that that's going to help job growth.

WHITEHOUSE: Remarks by the President on the American Jobs Act

But a perennial challenge has been in getting the water clean enough that it can be reused in the next frack job or simply discharged down a river or stream.

FORBES: Shale Gas Frackers Get Excited About ... A New Sponge?