求教一道逻辑题

hippoma

1.“Life expectancy” is the average age at death of the entire live-born population. In the middle of thenineteenth century, life expectancy in North Americawas 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 theprime of life.
Which of the following, if true, undermines theargument above?
(A) In the middle of the nineteenth century, thepopulation of North America was significantlysmaller than it is today.
(B) Most of the gains in life expectancy in the last150 years have come from reductions in thenumber of infants who die in their first yearof life.
(C) Many of the people who live to an advanced agetoday do so only because of medical technologythat was unknown in the nineteenth century.
(D) The proportion of people who die in theirseventies is significantly smaller today than is theproportion of people who die in their eighties.
(E) More people in the middle of the nineteenthcentury engaged regularly in vigorous physicalactivity than do so today.

答案是B,想不明白。。。。。有同学能给解释下不

Fiona09

首先，题干介绍了life  expectancy的概念。然后，接着说在19世纪中叶，北美的平均寿命是40岁，而现在是80岁。因此推出，在那些年，人们对于老的观点不同，就是在那时候他们认为老的年纪我们现在认为是年轻的。求削弱~~

B项是说最近这150年以来，平均寿命的增长是源于婴儿第一年死亡率的下降。也就是说其实19世纪中叶的人并不是因为短寿，而是因为初生婴儿的死亡率高导致整个人口平均寿命变短了。属于他因削弱，所以是正确选项。

hippoma

Fiona09 发表于 2017-4-27 15:38
首先，题干介绍了life  expectancy的概念。然后，接着说在19世纪中叶，北美的平均寿命是40岁，而现在是80岁 ...

谢谢啦

RRZZR

这题实际上就是要求你理解people considered old是什么意思

ppl considered old是指 “还活着的人”里面年龄较大的，而不是 “所有被生出来的人不管活着的还是死了的”里面年龄较大的。