Which best explains how the supremacy clause is connected to federalism?

The correct answer here is that the supremacy clause states that the federal government has more power than the state governments.

in the constitution of the united states, the supremacy clause is to be found in article vi, clause 2 where it states that the constitution is the highest legal document of the state and the federal laws that are made in accordance to it are the supreme laws of the land. this means that in a conflict between the federal and state laws, the federal laws, if constitutional, take precedence over the state laws. 

The best statement that explains how the supremacy clause is connected to federalism is : the supremacy clause establish that the federal government has more power than the state government.

which mean that in case there was a conflict of law between the federal government and the state government, the federal law is prioritized because of this clause

Because the discoveries were some of the oldest human remains.