If a country has a large elderly population together with very low fertility, which long-term concern may arise?

Correct answer: Shrinking working-age population

Very low fertility means that fewer children are born and that younger generations become smaller. At the same time, a large elderly population means that many people are moving out of working ages or require support. Over the long term, fewer young people will enter employment while the number of older people remains large or grows. This can reduce the size of the working-age population and increase pressure on pensions, health services, families, and public finances. Therefore, option A is correct.

The other choices describe opposite or unrelated effects. Very low fertility does not rapidly expand the child population, so it is unlikely to create excessive demand for schools. Youth dependency would generally fall rather than rise sharply. A return to the first stage would require high birth and death rates, which are not indicated here. The concern is a changing age structure and a possible shortage of workers relative to dependents.