Answer:
The correct answer is A. The modern United States regime shares power between the states and national government, making it an example of a federal system.
Step-by-step explanation:
Federalism is a political system in which political and administrative power is distributed between two levels of power.
On the one hand, there is a federal government, which is in charge of centralizing the most important tasks of the nation, thus taking care of issues in a national level. For example, the distribution of money between states is a federal task, that is carried out directly by the Federal Government and the Congress, through the approval of the Federal Budget. This task could not be taken by the states, since states are not allowed to regulate or legislate about other states.
On the other hand, there are different subdivisions within the nation, that act separately, each one having its own tasks in its own territory. This is the state level, in which each state takes care of its own business in its territory, for example, school administration in a state territory.
As we can see, in federalism there are two levels of power, that coexist peacefully and need each other in order to function correctly.