Read the following passage and answer the item that follows. Your answer to this item should be based on the passage only.

A country entering a youth bulge, where working-age adults temporarily outnumber children and the elderly by an unusually wide margin, gains a window in which relatively few dependants must be supported per worker. Nations that have converted this window into faster growth, from East Asia's earlier experience to more recent examples elsewhere, share one feature: heavy, early investment in schooling and vocational skills for the very cohort entering the workforce. Where that investment lagged, the same demographic bulge instead produced a large pool of under-skilled job seekers competing for too few suitable openings, turning a potential asset into a source of social strain.

Which of the following would invariably happen once a country's youth bulge window opens?