Concept:A federal state divides power between a central government and regional governments. This division needs constitutional protection.
Explanation:A rigid constitution is difficult to amend because it requires a special procedure or a supermajority.
This makes it suitable for a federal state.
It protects the agreed division of powers from sudden or careless changes.
It also prevents the central government from easily overriding the autonomy of states.
In contrast, a flexible constitution can be amended easily.
That would make the federal structure unstable and weak.
Republican and parliamentary constitutions refer to the form of government, not the amendment process.
Therefore, a federal state is best governed under a rigid constitution.
Answer:B. rigid constitution