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【B11】
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【B8】
【B4】
【B5】
Nature has s prefect system for recycling water. Water is used again and again. It falls as rain.【B1】it goes one of three places. It might seep slowly through the soil【B2】it soaks through into the natural reservoirs【B3】. It might disappear into the air by【B4】quickly. It might【B5】into streams to rivers and to the oceans.
There is a problem【B6】this recycling system. It is a balance that can be easily【B7】by people. Nature's recycling system can work well【B8】people work with the system-not【B9】it. Some ways that people【B10】with nature are easy【B11】. Dirty sewage water from homes and factories must not【B12】with drinking water. People would get sick from drinking dirty water.
【B13】other ways that people hinder nature. Some of these ways are not so easy to understand.【B14】, a marshy bog(沼泽) may not be good for everything, but it【B15】an important purpose. The soft and wet soil of a bog【B16】water to reach the underground reservoirs. What happens to the balance of nature if the bog is filled in？ Many housing development projects have been built【B17】marshes once were. The【B18】of the houses are likely to have problems. They are likely to【B19】water, to flood in【B20】seasons. Huge storm sewers are built to carry away with the water from wet areas. These huge pipes prevent wet basements in the houses of the community.
【B1】
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