题目选项分析

"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?

【选项】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.