2. In the years since the city of London imposed strict air-pollution regulations on local industry, the number of bird species seen in and around London has increased dramatically. Similar air-pollution rules should be imposed in other major cities.
Each of the following is an assumption made in the argument above EXCEPT:
(A) In most major cities, air-pollution problems are caused almost entirely by local industry.
(B) Air-pollution regulations on industry have a significant impact on the quality of the air.
(C) The air-pollution problems of other major cities are basically similar to those once suffered by London.
(D) An increase in the number of bird species in and around a city is desirable.（A）
(E) The increased sightings of bird species in and around London reflect an actual increase in the number of species in the area.
这题偶怎么也想不通A答案好在哪里，笨 ：(如果这些主要的城市不是因为工业污染了空气的作为假设的话，那又什么必要推行那个控制污染的条例呢？
19. The U.S. census is not perfect: thousands of Americans probably go uncounted. However, the basic statistical portrait of the nation painted by the census is accurate. Certainly some of the poor go uncounted, particularly the homeless; but some of the rich go uncounted as well, because they are often abroad or traveling between one residence and another.
Which of the following is an assumption on which the argument above depends?
(A) Both the rich and the poor have personal and economic reasons to avoid being counted by the census.
(B) All Americans may reasonably be classified as either poor or rich.
(C) The percentage of poor Americans uncounted by the census is close to the percentage of rich Americans uncounted.
(D) The number of homeless Americans is approximately equal to the number of rich Americans.（C）
(E) The primary purpose of the census is to analyze the economic status of the American population.
请大家帮忙解释一下这题为什么选C，我觉得其它的答案都很牵强，所以选了这个，但是思路不是很清楚。多谢了。
"In most major cities, air-pollution problems are caused to a significant extend by local industry." is a necessary assumption for the argument, but not A. A, "In most major cities, air-pollution problems are caused almost entirely by local industry.", is too extreme. The argument does not need such an extreme assumption.
Q19: "the basic statistical portrait of the nation painted by the census is accurate"
What is a statistical portrait? If you have already reviewed math, you know that things such as mean, standard deviation, are considered statistical portraits. Look at how these statistical data are calculated and you will see why C is the best answer.
第一题，robertchu同志说的很对：）
我说说Q19: 题目说那些Basic statitics数据还是准确的，因为穷富相抵的原因。
那么，我们说这个结论是对的前提，最基本的要能证明：穷富确实相抵了。如何保证呢，C选项说穷富各自没被普查到的rate相同，就可以的了。
Robertchu and Cuteishere, I got it, thank you very much
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