People are working hard to find ways to keep the earth clean: they treat waste gases, protect water sources and purify waste water.
人们努力寻找方法保持地球清洁：他们对待废气，保护水源，净化废水。
The earth seemed too earthy for him, with too little water to keep it sufficiently clean; so that he had to be in a constant state of warfare with its chronic soiled state.
在他眼里，大地似乎显得太过于泥土气了，水也显得太少，以致不能使土地够得上干净；因此他得不断地与这惯常的尘土状态作战。
The oceans are important to all animals on the Earth. We must keep them clean. We must stop polluting them.
海洋对于所有的地球上的动物都有着极其重要的意义。我们要保证清洁，禁止污染。
The oceans are important to all animals on the Earth. We must keep them clean. We must stop polluting them.
海洋对于所有的地球上的动物都有着极其重要的意义。我们要保证清洁，禁止污染。
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