In what way do the states serve as laboratories for federal policy? a. The Supreme Court regularly tests the validity of state laws.
b. States introduce laws that the federal government adopts.
c. States are allowed to choose which federal laws to enforce.
d. Federal hospitals provide regional data for fighting diseases.

Laboratories of democracy is a phrase popularized by U.S. Supreme Court Justice Louis Brandeis in New State Ice Co. a diverse patchwork of state-level government practices is created. If any one or more of those policies are successful, they can be expanded to the national level by acts of Congress.

Explanation:

radioactive dating, also known as  radioisotope dating  is a process that in  estimating the approximate  age  of  rocks. these data can be analyzed from  the studies dealing with the  decay of the radioactive elements that are present in these rocks. in nature, there are a few types of materials or atoms which are quite unstable and they spontaneously decay or breakdown to form other kinds of atoms.