A. Stop states from passing certain laws.
Federalism is a system of government in which power is divided between the central government and regional or state governments. This division of power helps limit the power of the federal government by denying it the ability to completely control state governments and preventing it from infringing upon the rights of citizens within individual states. This means that while the federal government has certain powers granted to it by the Constitution, it cannot interfere with the ability of state governments to pass laws that are not in violation of the Constitution. This is an important aspect of federalism, as it ensures that states have a degree of autonomy and can serve as laboratories for policy experimentation, while also helping to prevent an overly powerful federal government.