Final answer:
Federalism is a system of government where different levels of government share authority. D. Different levels of government share authority over the same area and people.
Step-by-step explanation:
Federalism is a system of government in which power is divided between a central or national government and state governments. It can be best described as D. Different levels of government share authority over the same area and people. In a federalist system, the national government and state governments each have their own areas of jurisdiction and share powers in governing.
For example, in the United States, the federal government has powers such as regulating interstate commerce and conducting foreign relations, while state governments have powers such as setting and enforcing driving laws.