Although the fertility rate for women in the united states has declined in recent years to a value below replacement level, the united states population is still increasing because of lower average age at first marriage
a lower infant death rates
b increased longevity
c improved health care
d immigration e submit

B) Increased longevity

Explanation:

Couples getting married earlier in their lives will always result in a longer time in which they could have a kid. Being married and trying for kids longer gives more of a chance to have one and over that extended period of time all it takes is the right circumstances and any non-infertile couple could get pregnant. People also live longer today than they did years ago which would also be grounds for increased longevity.

the first option is ur answer : )

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