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题库 / Prep2007E1-CR-26
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?
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.
For several decades, Megacity, as distinct from the countryside, has had a steadily declining birth rate.
Cities smaller than Megacity have also experienced sustained population growth.
The great majority of immigrants to Remsland settle in Megacity, at least initially.
Megacity has long offered better employment prospects than most rural areas.
错选A
人口增长率=出生率-死亡率，因此两个方向，要么1）M的死亡率因为新的原因上升了，要么2）M的出生率下降了。
A选项虽然说出了新的主要原因是vehicular traffic，但并没有明确指出因为这个原因死亡率比以前要高了，因此可以排除；B选项出生率下降了，正确。
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