Question

what must all governments in the united states follow, according to article vi?
the declaration of independence
the laws of the most populated state
the constitution

Explanation:

Article VI of the US Constitution establishes the supremacy of the Constitution, federal laws, and treaties. So all governments (state, local, federal) must follow "The Constitution" as it is the supreme law. The Declaration of Independence is a founding document but not the supreme law, and "The laws of the most populated state" is incorrect as no state's laws supersede the Constitution.

Answer:

The Constitution