我知道好像这题很简单，但是还是有点不明白~~og12 cr 1

shkyxy

“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, whereas 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 the 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 reductions in the number of infants who die in their first year of 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 proportion of people who die in their seventies is significantly smaller today than is the proportion 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.
B怎么和结论联系起来呢，A,D感觉是support但是不知道怎么解释，谢谢前辈们啊，急啊

sdcar2010

Two group of people were born at the same time. In the first group, five infants died at age of 1. The other 5 died at the age of 79. The average age at death for the group is 40 years old.
In the second group, all ten people died at the age of 80. The average age at death is 80. In group one, what age do you consider is an old age? 79. Not 40.

leweiyang

其实argument的结论意思就是，平均死亡年龄（entire live-born ）现在比过去高，意味着现在的人平均寿命，普遍年龄都很高。
削弱：在整个基数里，幼年死的人比例大（老年死的人比例小）平均死亡年龄低（40岁）；幼年死的人比例小（老年死的人比例大）平均死亡年龄高（80岁）。两个情况下都有死于年纪很大的或年纪很小的人。不一定就是大家都很长寿的缘故。
A：光告诉我基数，没用。
B：从过去到现在，幼年死的比例变小，所有才有题目中80>40的现象。所以40岁可以同样都觉得很老啊。
C：现在的人因为医疗好普遍都长寿，没削弱。
D：80岁的极端是1岁，就像楼上说的。70岁跟80岁比，可能也是因为医疗好，大家在医院里挨了十年才死，普遍都长寿，没削弱。
E：过去的人更多的在锻炼身体，没讲清楚，判断不了削弱还是支持。

各抒己见吧，同努力！

sdcar2010

LS, 40 years old is not OLD in either now or before, according to B.

xxpatzz

别人的解释，我觉得很好


"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, whereas 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.

b) Most of the gains in the life expectancy in the last 150 years have come from reductions in the number of infants who die in their first year of life.

Conclusion: People in older times (middle of 19th century or 150ish yrs ago), must have been considered old at an earlier age (e.g. someone who was 40 yrs old was considered old 150 yrs ago, which is considered a prime age now).
B says, the average age at death has increased now because of lower infant death rates from 150 yrs ago. Thus, bringing the average age at death up in today's date.

Think of this as an Average/Mean problem in Quant, if a majority of elements in a set are 0, it brings the average down, when the 0 value elements are excluded, it brings the average up.

Does that help?

crack25

想问一下，我怎么觉得D更多的是不能确定是削弱还是支持，因为他没说10 20 40 .。。等等这些年龄的情况，或许某一个高或低，结果就可能削弱/可能支持。
欢迎拍砖
看了一下，原文还有80岁，抱歉
D选项，如果现在人70岁挂掉的比率明显小于80岁挂掉的比率，而平均寿命又是80岁的话，可想应该会有很高比率的人90岁多才挂掉。或者更统计点说，出现极小值时，平均值被低估了，实际的平均寿命甚至高于80岁。结论很显然被support了。
其实D选项跟B选项是一个原理，只是一个是低估以前的40岁均值，所以WEAKEN了；这个是低估现在的均值，所以SUPPORT了

keline1991

ls分析的思路很靠谱，终于懂了！

InfiniteAlex

其实挺好想的，一个阶段某地区的life expectancy是该地区所有人群life expectancy平均数。B选项直接weaken结论。