In the United States, the Federal Government and the State

In the United States, the federal government and the state and local governments share power with one another. In some instances, the federal government has powers that the state governments do not have and the states have power the federal government does not have, while in other instances the state and federal governments share power. This is an example of which system of government?

A) federalism
B) unitarian
C) confederation
D) authoritarian