Prep 058&004365一道逻辑解释题

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.

大家帮看看，为什么选B， A为什么不行呢？

结论加强，说明为什么移民持续增加，但M城人口增长率却没有大量增加？

显然移民数量只是人口的一小部分，还有诸如犯罪，天灾等等很多因素。答案B从出生率下降的角度加强了结论。所以为佳。

A说M城卫生死亡率高于交通死亡率，但并没有说明和移民相比是什么情况，即如果移民进入的数量远远大于死亡率的话，M城人口还是应该大量增长的。

我觉得可以这样理解：A选项其实是削弱。

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

意思是过去导致死亡率的卫生不良在程度上要比现在导致这个城市死亡率的交通事故来的大。

又因为如果在高的死亡率下，M的人口都会因为外人的加入而增多，那么相对死亡率低的时期 + 再结合原文中的“有更多的移民不断进入“，那人口增长率不是应该高了么？

所以无法解释题目的结论

）

同志们，多谢多谢啊！

解释得很清晰，我明白了。