Concept:Rural-urban migration is the movement of people from villages to cities, often causing serious problems in developing countries.
Explanation:In developing countries, economic opportunities like jobs, business, industries, and social amenities are mostly located in urban areas.
Because of these better opportunities, many people move from rural areas to urban centres.
This large movement creates overcrowding, unemployment, housing shortages, and pressure on public services in cities.
Therefore, rural-urban migration is a major problem for developing countries.
Answer:A. Rural-urban migration