GMAT备考，除了背背背，更重要的就是练练练！通过练习，巩固知识，熟练技巧，最终才能在GMAT考试中发挥出色，取得好成绩，所以练习的重要性不言而喻。因此，小编为大家精心准备了GMAT考试各类题型的练习题和答案解析，帮助大家每日一练，为考试做好准备。一起来看今天的题目吧。
今日练习题为逻辑题，题目如下
"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.
正确答案：
B
题目分析：
原文先介绍了life expectancy的概念，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，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weaken。
选项分析：
A 在十九世纪中叶，北美的人口怎么着，原文从头到尾都在讨论寿命问题，没讨论人口，排除。
B 说明以前的平均寿命低是被新生儿高死亡率拉低的。有效weaken，正确
C 没说到medical technology，并且也不能有效weaken，排除。
D proportion没说到，weaken无效，排除。
E 没说体育锻炼，且weaken无效，排除。
