今天刚开始做OG 11的逻辑就遇到困难! 请大家帮忙解决以下！！1

"Life expectancy" is the average age at death of the entire live-born population. In the middle of the nineteenth

century, life expectancy in North America was 40 years, wherreas now it is nearly 80 years. Thus, in those days,

people must have been considered old at an age that we now consider the prime of life.

Which of the following , if true, undermines the argument above?

A. In the middle of nineteenth century, the population of North America was significantly smaller than it is today.

B. Most of the gains in life expectancy in the last 150 years have come from reduction in the number of infants

who die in their first year life.

C. Many of the people who live to an advanced age today do so only because of medical technology that was

unknown in the nineteenth century.

D. The propotion of people who die in their seventies is significantly smaller today than is the proportiion of people

who die in their eighties.

E. More people in the middle of the nineteenth century engaged regularly in vigorous physical activity than do so

today.

我应该从哪里入手解这个问题呢？

答案是b 

因为 新生儿的年龄是0 如果他们出生了就死的话 就相当于在Life expectancy 的 分子加 0 ,而 分母加1

这样Life expectancy就会变低

但这并不能代表 prime of life in the middle of the nineteenth 比现在低.....

PS: 要是解释的不好请原谅....

答案确实是b；

但我对以下2句话看不明白到底是什么意思? 请继续帮忙解释一下！！！

1。Thus, in those days, people must have been considered old at an age that we now consider the prime of life.

2。Most of the gains in life expectancy in the last 150 years have come from reduction in the number of infants who die in their first year life。

1,所以,在那个时候,我们现在认为的黄金年龄肯定被视为老年了.

2,(个人理解)近150年来大多数生命周期的获得都是来源于一年内新生儿死亡数目的下降...(言下之意,是说以前平均生命年龄低是因为婴儿死得太多了,摊低了平均...存活下来的人不一定比现在die早)

1.再那段时间里,在人们本来认为很老的年龄,在我们现在看来而是壮年

2.在过去的150年里,年龄的期待值的增加是由于新生儿在出生第一年的死亡率降低了