OG11-3 请教！！！

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.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

我也想不通这题目

B

LE是对广大人民群众死亡时年龄的平均值

婴儿出生就死掉的话，肯定造成平均值的大幅降低。从而40岁就是LE了。其实那时候活到70岁的人多了去了，就是婴儿死亡率拖了这个平均值的后腿。

现在婴儿都能活到老了，平均值自然上去了。

which of the following, if ture, undermines the argument above?

削弱的是argument（论证过程，论点),不是结论。