What have many political scientists called laboratories of democracy? a. congressional committees b. local governments c. the executive agencies of the federal government d. the states e. special districts?

the states

The term “Laboratories of democracy”  is popularized by U.S. Supreme Court Justice Louis Brandeis to describe how a state may function as a laboratory where it can   do social and economic experiments without risk to the other states. If they work, then other states will use them. And perhaps even the entire country, will use them.

explanation:

the addition to geographic boundaries that might have  kept the people of the huang river civilization from traveling to far distance region is that they had learned about the other river valley civilizations but feared contact would bring invasion.

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