Concept:Federalism in Nigeria began when the country was divided into administrative regions with separate governments under one central authority.
Explanation:The Richards Constitution of 1946 is credited with laying the foundation of Nigerian federalism.
Before it, Nigeria was administered as a single unit.
In 1939, Governor-General Bernard Bourdillon split the Southern Provinces into Eastern and Western Provinces.
However, it was his successor, Sir Arthur Richards, who gave this arrangement a constitutional basis in 1946 by creating three regions: the Northern, Eastern, and Western Regions.
Each region had its own House of Assembly, while a central Legislative Council remained at the centre.
This dual structure of regional and central governments is what started Nigeria on the path of federalism.
Answer:D. Richards Constitution