The correct answer is: "power split and shared between the central and state governments".
The US Constitution ennumerates the powers which are reserved to the federal and state goverments. After several landmark Supreme Court rulings, the necessary and proper clause was also included in the US Constitution, giving implied powers to the federal goverment that are not explicitly contained in the Constitution. It also describes the supremacy of the federal goverment over state goverments, that cannot easily interfere with the actions of the first.
