ChinaHawk

The passage states that because "In the middle of the nineteenth

century, life expectancy in North America was 40 years" so => "Thus,

in those days, people must have been considered old at an age that

we now consider the prime of life." The conclusion can be true if

people in North America in nineteenth century usually died around

40( life expectancy at that time).

B. undermines the conclusion by saying that the life expectany does

not reflect how long people could live at that time correctly,

because there is another issue we should consider -> "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. says that people can live longer today only because new medical

technology which did not exist in 19th. It does not mention anything

about the age of poeple in 19th. It only proves that 1. people live

longer today, and 2. there was no such medical technology in back

days. Therefore, it has nothing to do with the argument, or you can

say it supports the argument a little bit by pointing out there was

no advance medical technology in 19th, which might cause people died

early.