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专八作文范文:水的净化
专八考试中考生们最为重视的就是专八作文,专八作文不仅需要考生对词汇及语法的熟悉运用更是对考生思维拓展的一项考察,新东方在线专八频道整理了一系列专八作文范文供考生们参考练习。
水的净化(water purification)
the provision of safe water necessitates one of the rnajor expenditures of manpower and revenue in our modern cities. the purification of water is basically a two-step or three-step process carried out under the strict supervision of public health scientists and engineers. as the first step, natural water from the least contaminated source is allowed to stand in large reservoirs, where most of the mud, clay, and silt settle out; this is called "sedimentation". often in water with high mud content, lime and aluminum sulfate are added to the water in the settling reservoirs. these chemicals react in the water to form aluminum hydroxide, which settles slowly and carries much of the suspended material, including most of carries much of the suspended material, including most of the bacteria, to the bottom of the reservoirs. as the second step, the water is filtered through beds of sand and grovel, which remove other impurities and chemicals in it. during or after filtration, chemicals are ordinarily added to the water to kill any remaining harmful bacteria. chlorine is one of the most common chemicals used for this purpose. a third step taken by some rmnicipalities is adding to the water other beneficial chemicals such as fluoride to make tooth enamel hard, and soda ash to make the water itself soft. the water purification process, carried out with little variation from one large city to another, is perhaps the biggest factor in the prevention of major outbreaks of disease in this country.
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专八听力训练:时政短语热点【word版】
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专八翻译模拟练习题总结
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专四专八写作必备高级词汇
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专四听力听写练习50篇文本文档
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2021专四写作高级范文15篇集锦
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专八基础词汇积累完整版(169页全)
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英语专业四级词汇PDF电子版
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近十年专八真题答案及听力原文
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近十年专四真题答案及听力原文
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