If the birth rate is falling but total births are high, what is the most likely reason?

Correct answer: The reproductive-age group is large

The correct answer is A: a large reproductive-age group can produce many total births even when the birth rate is falling. A rate is a proportion or measure relative to a population, whereas total births are the actual number of babies born. Step one: the birth rate decreases, meaning the average or proportion of births is lower. Step two: if the number of people in the reproductive-age group is very large, even a lower rate applied to that large group can result in many births. This is sometimes called population momentum. A is correct because population size and age composition affect the total. B is wrong because the death rate does not determine how many births occur. C is wrong because migration being possible or impossible is not the main explanation. D is wrong because a large land area does not itself produce births; the number and age structure of people matter. Memory cue: a lower rate multiplied by a much larger base can still give a high total.