If a country's 50 to 59 age group is very large while the 20 to 29 age group is relatively small, which challenge is most likely over the next decade?

Correct answer: Pressure from elderly dependency and labor-force replacement

A large 50–59 age group is close to retirement or old age. During the next decade, many members of this cohort will enter the 60-plus group, increasing the number and likely the share of elderly dependents. A relatively small 20–29 group also means that fewer young adults may be available to enter jobs and replace retiring workers.

Together, these features can create pressure on pensions, health and care services, and the supply of new workers. Therefore, option B—greater old-age dependency and pressure to replace the labour force—is the most likely challenge. A school-demand explosion would require a large rise in births, which is not indicated. Fertility will not necessarily rise, and the working-age population cannot automatically double.