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英语四级作文700字：干旱的世界(A Thirsty World) the world is not only hungry, it is also thirsty. this may sound strange, since nearly seventy percent of the earths surface is covered with water. but about ninety percent of this is sea water. man and most of the animals can only drink and use the remaining percent of water--fresh water. the need for water is increasing day by day. only steps are taken to deal with this problem immediately can we avoid a severe world-wide water shortage later on. one of the first steps is to develop ways to reuse it. eperiments have already keen carried out in this field.the used witer has been pumped to a water-purifying plant.there, it can be separated from waste matter and treated with chemicals so that it can be used again, just as if it were fresh water from a spring. |