OG11逻辑第3题

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.

我的感觉是B,C都可以。答案是B。
为什么不选C呢？求教！书上的解释只有一句，说C supports the argument.