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  3. If you live in a city in North America or Europe, you have probably never thought much about water. Whenever you need some, you

If you live in a city in North America or Europe, you have probably never thought much about water. Whenever you need some, you

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问题      If you live in a city in North America or Europe, you have probably never thought much about water. Whenever you need some, you turn on the tap and there it is. Millions of people in other parts of the world are not so lucky. They have trouble getting enough clean water for their basic needs. This situation may soon become common all around the world, scientists believe. In fact, they say that the lack of clean water may be one of the biggest issues in the twenty-first century.
     The reasons for this are clear. On the one hand. people are using more water than ever before. Over the last fifty years, the population of the world has more than doubled. On the other hand, many sources of surface water such as rivers, lakes, and streams are too polluted and unhealthy for use as drinking water.
     This has forced more and more people to drill wells so they can get water form underground. There are enormous amounts of water deep underground in lakes called aquifers. Until recently, scientists believed this underground water was safe from pollution. Then, in the 1980s. people in the United States began to find chemicals in their well water, and scientists took a closer look at what was happening. Weldon Spring, Missouri, for example, was the site of a bomb factory during World War Ⅱ. The factory was destroyed after the war. but poisonous chemicals remained on the ground.  Very slowly, these chemicals dripped down through the ground and into the aquifer. Once they did, however, the water form that aquifer was no longer drinkable.
   It probably never will be drinkable again, Underground water is not renewed regularly by the rain, like lake or river water. Thus, if a harmful chemical gets into an aquifer, it will stay there for a very long time. Furthermore, it is nearly imp6ssible to remove all the water in an aquifer and clean out the pollutants.
    Industrial sites like Weldon Spring are one cause of underground water pollution. There are thousands of such sites in the United States alone, and many others around the world. Underground water pollution is also caused by modern farming methods, which require the use of large amounts of chemicals in the fields. And finally, yet another important cause of underground water pollution is waste. That includes solid waste thrown away in dumps and landfills, and also untreated human and animal waste.
     The situation is indeed very serious. Fortunately, there are many aquifers and they are very large. Only a small number have been seriously damaged so far. But if the world does not want to go thirsty in the near future, further pollution must be prevented. Around the world, governments must make real changes in industry, agriculture, and waste disposal.  
We can infer from this passage that industry, farming, and waste are ______.
选项 A、polluting all aquifers in the United States
B、minor sources of underground water pollution
C、causing problems in bomb factories
D、the three main sources of underground water pollution
答案D
解析 推断题。倒数第二段“Industrial sites．．．are one cause of underground water pollution．．． Underground water pollution is also caused by modern farming methods，which require the use of large amounts of chemicals in the fields．And finally，yet another important cause of underground water pollution is waste”中清楚地说明了地下水污染的三大原因，即化学物质、农业化肥和废弃物。因此正确答案为D项。
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