Under which circumstance can a country's dependency ratio temporarily decline?

Correct answer: When a large youth cohort enters working ages and fertility declines

The dependency ratio compares people commonly considered dependent, such as children and older adults, with the working-age population. It can temporarily decline when a large group of young people enters working ages and fertility falls at the same time. Earlier high fertility may have created a large cohort, while lower current fertility produces smaller child cohorts. Consequently, the working-age share rises relative to the number of dependents. This is often the demographic setting associated with a possible demographic dividend, although employment and skills remain necessary.

Option A is correct because it combines the two relevant changes: a large cohort enters working ages and fewer children are born. Option B would increase the dependent share. Option C reduces the working-age population and tends to raise the ratio. Option D creates more children and therefore usually increases dependency. The decline is temporary because later ageing can increase old-age dependency again.