Answer:
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.