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  3. As a result of pollution, Lake Erie, on the borders of the U. S. A. and Canada, now does not have many living things. Polluti

As a result of pollution, Lake Erie, on the borders of the U. S. A. and Canada, now does not have many living things. Polluti

admin2012-04-07  76
问题    As a result of pollution, Lake Erie, on the borders of the U. S. A. and Canada, now does not have many living things.
   Pollution in water is not simply a matter of "poisons" killing large numbers of fish overnight.
   Very often the effects of pollution are not noticed until many months or years later because the first organisms (生物) to be affected are either plants or planktons (浮游生物). These organisms are the food of fish, birds, and other creatures. When this food disappears, the fish and birds would die too. In this way a whole food chain can be wiped out, and it is not until dead fish and water birds are found at the river’s edge or on the sea shore that people realize what is happening.
   Where do the substances that pollute the water come from? There are two main sources, sewage (生活污水) and industrial waste. As more detergent (洗涤剂) is used in the homes, more of it is finally put into our rivers, lakes and seas. Detergent harms water birds by breaking down the natural substances which keep their feathers waterproof. Sewage itself, if not properly treated, makes the water dirty and prevents all forms of life in rivers and the sea from receiving the oxygen they need. Industrial waste is even more harmful since there are more highly poisonous materials in it, such as copper and lead.
   So, if we want to stop this pollution, the answer is simple. Sewage and industrial waste must be made clean before flowing into rivers and seas. It may be already too late to save some rivers and lakes, but others can be saved if the correct action is taken at once.
The living things die because there is no ______ in the river or sea.
选项 A、oxygen
B、poison
C、water
D、fish
答案A
解析 细节题。根据第三段倒数第二句“Sewage itself, if not properly treated, makes the water dirty and prevents all forms of life in rivers and the sea from receiving the oxygen they need”(如果不对污水进行适当处理，就会污染水源，而且使水中的各种生物得不到它们所赖以生存的氧气)，可以判断生物死去是因为缺少氧气。此外，本题也可以运用常识作答。所以答案是[A]。
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