Concept:Dual citizenship was a distinctive feature of the French colonial policy of assimilation in West Africa.Explanation:The French colonial government offered dual citizenship to its West African subjects.This arrangement granted them citizenship of both France and French West Africa.At first, it was limited to subjects from the Four Communes in Senegal.Later, the policy was extended to all French West African citizens.No other colonial power listed in the options practised this dual citizenship system.Answer:D. French colonial system