Question

　
E　　
As a result of pollution , Lake Erie , on the borders of the USA and Canada, is now without any 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 for many months or years because the first organism(生物体 ) to be affected are either plants or plankton. But these organisms are the food of fish and birds and other creatures. When this food disappears, the fish and birds die too. In this way a whole food chain can be wiped out, and it is not until dead fish and water birds are seen at the river’s edge or on the sea shore that people realize what is happening.　　
Where do the substances which pollute the water come form? There are two main sources sewage (污水) and industrial waste. As more detergent (洗涤剂 ) is used in the home, so more of it is finally put into our rivers. lakes and seas. Detergents harm water birds dissolving 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 many highly poisonous things in it, such as copper and lead(铅 ).　　
So , if we want or stop this pollution , the answer is simple: sewage and industrial waste must be made clean before flowing into the water. It may already be too late to save some rivers and lakes, but others can still be saved if the correct action is taken at once.　　
72. Pollution in water is noticed _____. 　　
A. when the first organisms are affected    B. when a good many fish and birds die 　　
C. when poisonous things are poured into water      　　
D. as soon as the balance of nature is destroyed 　　
73. The living things die because there is no ____ in the lake or river.  　　
A. water          B. fish               C. poison           D. oxygen 　　
74. Which of the following is harmful according to the passage? 　　
A. Organisms                             B. Plants and plankton in the water     　　
C. Waste water from cleaning   D. Industrial waste made clear before flowing into the water 　　
75.The way to stop water pollution is _______.　　
A. realize the serious situation clearly 　　
B. put oxygen into the river 　　
C. make the waste material harmless before flowing into the water 　　
D. make special room in the sea for our rubbish　　

Answer 1

72—75 B D C C 　　

解析