If net migration is zero but arrivals are mainly high-skilled young adults and departures are mainly lower-skilled older people, what effect is possible?

Correct answer: Human capital and working-age structure may improve

Zero net migration describes only the numerical balance between arrivals and departures. It does not mean that the two groups have the same ages, education, occupations, or skills. If more high-skilled young adults arrive while lower-skilled older adults leave, the total population may remain unchanged but its composition can improve. Hence option A is correct: human capital and the working-age structure may improve.

For example, equal numbers entering and leaving produce net migration of zero, but the incoming group may add workers, qualifications, and productive capacity, while the departing group removes fewer working-age people and more older dependants. This can alter the labour supply and average skill level without doubling the population. The change in natural increase is not fixed by this information, so option D is too strong. Option C wrongly assumes that a zero total balance means no demographic effect.