If a country's child population is steadily declining, demand for which service may fall after some years?

Correct answer: Demand for primary schools

Children usually enter primary school at a fairly predictable age, so a sustained fall in the child population will eventually reduce the number of new pupils. The effect is not always immediate: children already enrolled may continue for several years, and migration or changes in enrolment rates may alter the outcome. After this time lag, fewer pupils can mean less need for new classrooms, teachers, and some primary schools, especially in areas where the decline is large.

Choice A is correct because primary education serves the age group that is shrinking. Demand for pensions, geriatric medicine, and long-term elderly care is more likely to rise as the population ages, not fall because there are fewer children. The question asks about a likely service effect after some years, so the timing condition supports the school-related answer rather than an instant change.