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追梦爱我

26. (31045-!-item-!-188;#058&004365)

The population of Megacity, a sprawling metropolis in Remsland, has grown at a fairly steady rate for over a century.  A hundred years ago, poor sanitation in the city caused high mortality rates among the city's inhabitants, and what fueled the population increase was immigration from rural villages.  This immigration has continued and even increased.  Moreover, in recent decades, city sanitation has improved enormously.  Yet the city's population growth has not significantly accelerated.

Which of the following, if true, most helps to explain why the city's population growth rate has not changed?

(A) Mortality rates that were associated with poor sanitation in Megacity a hundred years ago were orders of magnitude higher than are mortality rates associated with vehicular traffic, which is currently a major cause of death in the city.
(B) For several decades, Megacity, as distinct from the countryside, has had a steadily declining birth rate.
(C) Cities smaller than Megacity have also experienced sustained population growth.
(D) The great majority of immigrants to Remsland settle in Megacity, at least initially.
(E) Megacity has long offered better employment prospects than most rural areas.

答案是B。

我的疑问是，A和B一样，也是给出他因来说人口为什么还是没有明显增加。为什么B对，而A错呢？
A.一百年前因为卫生太差而死的人比因为车辆事故而死的人多，在城市中因为车辆事故而死亡目前是死亡的主要原因。
B.几十年来，M市与农村不同，一直出生率不断降低。

追梦爱我

已经知道了

xiangfeidewo

能解释下吗

benpiao

说一下吗，到底A为什么错，是因为大一个数量级，现在的车祸无论如何也不能赶上？

benpiao

我觉得是不是，A没有体现一个下降或上升的趋势。

pumpkinhuo

A说的是一百年前M城因卫生条件差而导致的死亡率远远高于现在车祸引致的死亡率，而车祸致死现在成为M城的首因。按A的说法，M城人口应该增加才是（现在的死亡率下降了）。
            

Ailsa灵幽幽

人口增长率没上升，而死亡率可能下降了，还有移民到此的贡献，就应该想人口增长受两方面影响，一个是死亡数量一个是出生数量，既然死亡数量走不通，就应该从出生数量入手

一开始也选了A 现在觉得A无关

A 不管因为什么死，都是死

georgegeng

选A的人都做了一个假设，就是现在车祸死亡比100年前增加了很多很多（虽然这是现实，但是题目的情景中没有提到）。
假设以下的情况，100年前卫生原因一天死20人，车祸死1人(符合题目中说的orders of magnutide higher)，现在卫生原因一天死1人，车祸死3人(符合题目中说的currenty major cause of death)。 在别的条件不变的情况下（移民数量，出生率），人口应该增加。

[此贴子已经被作者于2009/8/7 23:56:32编辑过]