Concept:The middle belt of West Africa has sparse population due to historical and environmental factors, not industrial development.
Explanation:The middle belt experienced low population because of inter-ethnic wars, tsetse fly infestation, and the Arab slave trade in the north.
These factors caused insecurity, disease, and forced migration.
Concentration of industries would attract people and create dense population centers.
Therefore, it is not a reason for sparse population.
Answer:A. concentration of industries.