Concept:The Nigerian constitution adopts a presidential system of government with clear separation of powers among the three arms of government.
Explanation:Nigeria's current constitution is largely modelled after the United States Constitution.
This is shown by the establishment of three separate branches: the executive, the legislature, and the judiciary.
Each branch has distinct powers and can check the others through a system of checks and balances.
The President serves as both the head of state and the head of government, similar to the American President.
In contrast, the United Kingdom uses a parliamentary system, while Germany and France use parliamentary and semi-presidential systems respectively.
Therefore, the structure and operation of Nigerian government closely mirror the American model.
Answer:B. United States