Which process can reduce the working-age group in the source area?

Correct answer: Out-migration of young workers

The correct answer is A: out-migration of young workers. The working-age group consists broadly of people who are able to participate in economic activities. A source area is the place from which people leave. When young workers move from that area to another place for jobs, education, or other reasons, they are removed from the source area’s working-age population. This can reduce the available labour force and may create shortages in farms, factories, shops, or services. Option A is correct because it describes age-selective movement directly. Option B is wrong because the birth of children adds people to a younger age group, not immediately to the working-age group. Option C is wrong because in-migration brings people into the area and generally increases, rather than reduces, its population. Option D is wrong because a decline in death rate usually helps more people survive and does not specifically remove young workers. The effect is not always identical in every place, because the age and number of migrants matter. Memory cue: out-migration takes people out; in-migration brings people in.