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.
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.
C supports rather than weakens the argument?
and whether the meaning of argument and conclusion is the same?
我答案知道为什么,但我想问得问题是C 这个选项,为什么是加强而不是削弱....
这道题说的是年龄预期的问题。life expectancy
19世纪40岁 现在80岁 推出 现在认为是壮年的在当时认为是老年。
能weaken结论最可能的答案是对life expectancy的代表性有疑问，即切断前提结论的联系。
答案选项说婴儿死亡率现在很低正说明了当时的40岁并不能代表40岁时一定是老年人。
C中说，现代医学较过去发达了，说明40岁在当时很有可能是真的病死的年龄。从而建立了因果的联系。
（D）Theproportion of people who die in their seventies is significantly smaller today than is the proportion of people who die in their eighties.
新手上路，我不是很理解D，OG中说是support，但七十岁死和结论也没有关系阿，结论中说的是prime，对吧？
顶, 我也不懂OG对于C和D的解释
3. "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. :
Argument Evaluation
Situation Life expectancy for mid-nineteenth-century North Americans was 40 years; now it is almost 80.
at we think of as the prime of He must have been considered old in that earlier era.
Reasoning What point weakens this argument? The argument relies on the logic of having a great many more 80-year-old people in the population now than was the case 150 years ago. What would challenge this logic? The argument is built upon the average age at death and uses a definition of life expectancy that embraces the entire population of those born alive. What if, in the nineteenth century, the number of infants born alive but not surviving their first year was fu higher than it is today? Then the average age at time of death could be significantly reduced by a very large number of infant deaths. On the basis of such information about infant mortality rates, it would not be fair to assume that what today is considered the prime of life was in that earlier time considered old.
A The size of the population is irrelevant to the argument.
B Correct. This statement properly identifies the factor that undermines the argument: it was falsely assumed that age for an entire population was simply extended when actually the average age at time of death was significantly raised when the number of infants dying in their first year was reduced.
C This point supports rather than weakens the argument.
D This point supports the argument.
E The regular exercise of one of the two populations compared does not affect the argument.
The correct answer is B.
正确答案很好理解吧。就是个平均数的问题。
题目结论是 那个时候（19世纪中）的人在我们现在认为是壮年的年纪就被认为是老了
结论的基础是 那时候人平均寿命40岁，现在人平均寿命80岁。同时还隐含假设，这平均寿命是很好的衡量标准。
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
顶楼上的, 说的太好了!
原来用的是统计学的原理啊!
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