But it also has a second purpose-to keep the whole system clean.

另外它还有一个功能——保持整个系统的清洁。

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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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This paper introduced the effect of medium on the system pollution, analyzed the cause and put forwards the measure to keep the hydraulic system clean.

介绍了液压介质污染对液压系统的影响，分析了污染的原因，提出了保证液压系统清洁度的对策。

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But IMF official Marek Belka says Europe also must clean up its banking system.

VOA: standard.2009.04.24

He said more needs to be done to clean up the banking system.

VOA: standard.2009.04.26

But that does not mean he has given the new system a clean bill of health.

BBC: Don't forget tomorrow's nurses

Blaming the fact that staff used Linux operating systems on their production machines for "not noticing sooner", it advised concerned users to load some up-to-date antivirus software and "make sure your system is clean".

BBC: Scareware launched from tech blog

Do I want to invest in our people, in our middle class and making it stronger, and our infrastructure and our education system and clean energy -- is that one vision or are we just going to keep on doing the same things that got us into this mess in the first place?

WHITEHOUSE: Discussing the Economy in Albuquerque