[求助]prep1-26 疑惑

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。

大家能告诉我为什么A错吗？

同问

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）。

从题干得知，M城现在卫生条件改善，所以死亡率大大下降，而现在出现另一种情况：M城人口并未大幅增加，那么一定是有一个原因使得人口减少，B正好符合要求。