Explain national supremacy. what happens if a state law conflicts with a national law?

He Supremacy Clause and the Doctrine of Preemption. What happens when state law conflicts with federal law? The answer relies on the doctrine known as federalpreemption. The Supremacy Clause is a clause within Article VI of the U.S. Constitution which dictates that federal law is the "supreme law of the land."

Ithink it's c selection but i don't really know.