The most widely used system of government in the world is this one, in which the national government is supreme, and states and/or provinces exercise only the powers that the national government chooses to give them
A. Unitary System
B. Federal System
C. Socialist System
D. Confederation

a. the unitary system

Explanation:

wikipedia defines the unitary system as:

"A unitary state is a state governed as a single power in which the central government is ultimately supreme. The central government may create administrative divisions. Such units exercise only the powers that the central government chooses to delegate."

answer; they both highlight the power of the situation in determining behavior;

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