Which diagram correctly arranges system of government in order from least powerful to most powerful

The correct answer is C). Anarchy, Constitutional, Authoritarian.

When there is Anarchy in a system, it means that there is no control at all. It is the weakest power of government because it is assumed that the people do what they want to do and they don't have a government regulation.  

Constitutional is a stronger system of government that it’s limited by the Constitution and is a form of democratic system. Here, no branch of government has absolute power. The laws that are part of the Constitution regulates the social interactions.

An Authoritarian system is like a dictatorship government where the ruler has unlimited power. There are no other powers that balance the total exercise of the power of a Dictator.