我发现大家对OG11的讨论好少,我做到第3题就发现难以理解的问题了，搜索了也没看到

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 expentancy 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.

答案：B   哪位高手能够具体解释一下各个选项及原因吗？

还有一个小问题：OG11-6中的C选项：

C.A thorough survey of a planet's surface is insufficient to establish beyond a doubt that the planet contains no life.

这句话是什么意思呢？

 b是说，以前是Life expectancy低是因为在婴儿时期的死亡率很高（注意Life expectancy的概念）

而现在婴儿的死亡率变低了导致的Life expectancy高，这2个时期认为的所谓的old应该是差不多的

 呵呵谢谢，隔几天再看一遍这个题，居然都看明白了，看来思维是需要休息的。

但是第2个小问题还是不懂，由谁能够解释一下

A thorough survey of a planet's surface is insufficient to establish beyond a doubt that the planet contains no life.

这句话的意思呢？

Beyond a doubt 直译超过了怀疑，意译不怀疑、确定。

此句难在三重否定，直译“彻底的星球表面勘查不足以使不怀疑星球没有生命”。

意译“彻底的星球表面勘查不能够确定地球没有生命”。