What keeps this vast system clean is a web of earth, plants and animals; when water cannot be in touch with these it is no longer a sustainable and healthy system.

而能保持这一庞大水系统洁净的则是由泥土、植物、动物组成的网络。当水不接触它们时，这个系统就不能再保持正常了。

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He hastens to add that individual actions cannot be a substitute for the policy changes needed to curb emissions and promote clean energy.

他接着补充，个人的行动并不能取代政策的改变，而这些政策能促进温室气体排放的减少和清洁能源的开发。

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Fresh bread can be kept in a clean tin container. Be sure dust and insects cannot get to the bread.

新鲜面包可贮存在马口铁罐中，确保灰尘和昆虫无法进入。

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The quarry cannot be dredged to clean it because during WWII, the Germans who occupied the island used it as an armaments dump and tonnes of unexploded ordnance remain.

BBC: Torrey Canyon seabed returns to normal after oil spill

The officials reply that Rome was not built in a day, and they cannot be expected to clean up Houston overnight: after all, it took 30 years to get that way.

ECONOMIST: The Lone Smog State

The question is where do we do that, and the priorities cannot be to get away from clean energy.

WHITEHOUSE: Press Briefing