[讨论]机经一题逻辑请确认下是否是

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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.

Megacity大都市的人口在过去的一个世纪都在稳定的增长。一百多年前，城市的人口死亡率很高，人口上升是因为乡村人口的移民。这股移民一直持续并且增长。但是最近几十年，垃圾清理有了很大改善，但是人口却没有显著的增长。

文章推理：之前垃圾不清理，市民死亡率高，人口增长来自外部移民，并且移民在增长。最近垃圾清理了，但是人口却没有显著的增长。

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.

没有提到农村移民的增长，就算现在死亡率依然高，但是农村移民的增长也应该是的人口增长。和以前一样。

(B) For several decades, Megacity, as distinct from the countryside, has had a steadily declining birth rate.

正确，随着出生率的下降，人口移民和低出生率抵消了

(C) Cities smaller than Megacity have also experienced sustained population growth.

Cities smaller than Megacity，不能解释Megacity人口的增长缓慢

(D) The great majority of immigrants to Remsland settle in Megacity, at least initially.

只是说明了移民到Megacity，重复前提

(E) Megacity has long offered better employment prospects than most rural areas.

只能说明移民原因，不能解释人口增长减少