Concept:A unitary system concentrates power in one central government and is suitable where the population is homogeneous.Explanation:Some states adopt a unitary system because their citizens share similar culture, language, and history.This homogeneity reduces the need for complex power-sharing arrangements.In such states, a strong central government can govern effectively without regional divisions.Federalism becomes unnecessary when social differences are minimal.Thus, the main reason is homogeneity.Answer:B. of homogeneity