Concept:Sparse population is caused by conditions that make an area unattractive or unsafe for people to live in.
Any factor that attracts or retains people would not lead to sparse population.
Explanation:The middle belt of West Africa is sparsely populated due to historical, health, and security challenges.
Inter-ethnic wars forced many people to flee and discouraged permanent settlement.
Tsetse fly infestation spread sleeping sickness and limited farming and livestock keeping.
The Arab slave trade in the North removed many people from the region through raids and forced migration.
However, the concentration of industries attracts job seekers and encourages population growth.
Industrial areas normally become densely populated because people move there for employment and better living conditions.
Thus, concentration of industries is not a cause of sparse population; it is an exception.
Answer:D. concentration of industries