Federalism enables the states and the national government to share power.
The term "Federalism" means the power is divided between the national government and other governmental units, so that narrows it down to both A and B. However the question doesn't ask what specifically was adopted by the US in that. Federalism has been adopted by several countries such as Canada, Australia, Brazil, China, India, and more however all of those don't have the same three branches but share power based on states or provinces. Also I took the test and this is the right answer.
