Final answer:
In the American federal system, state and federal governments share power, but the federal government is supreme.
Step-by-step explanation:
In the American federal system, the best description is option C: State and federal governments share power, but the federal government is supreme.
Under the American federal system, powers are divided between the national government and the state governments. The national government has certain powers, such as coining money, declaring war, and establishing post offices, while the states have reserve powers better suited to being carried out by individual states.
Although state governments have their own powers, the federal government's laws ultimately have supremacy, meaning that if there is a conflict between state and federal laws, the federal law prevails.