If fertility declines for a long period in a country, which effect on age structure is most likely during the initial decades, other things remaining equal?

Correct answer: The share of children will fall and the relative share of the working-age group may rise

A long-term decline in fertility produces smaller new birth cohorts. As fewer children are born, the proportion of children in the total population gradually falls. For several decades, earlier large cohorts may still be moving through working ages, so the relative share of the working-age population can rise. This change can create a temporary opportunity for a demographic dividend if employment, health, and education are adequate. The effect is gradual, not an instant transformation of every age group.

Option A gives this likely early effect: the child share declines and the relative working-age share may increase. Option B is the opposite of the usual result. Older people do not immediately disappear; in fact, sustained low fertility can contribute to population ageing later. Age groups also do not become equal automatically. Therefore A is correct.