D) The class system of England
The Americans loved the way that England was run (besides the King and all the taxes) and they wanted to copy the class system of England.
The Americans knew almost nothing of the ancient Greek and Roman times. There wasn't enough information about the Greeks and Romans to know enough about their democracies, so obviously that answer is incorrect.
Let's just say that New England isn't a place you would go for a small town life. So, quickly we can scratch that option off.
Lastly, I have no idea what the Iroquois League is and I never learned about it while studying the Southern colonies of America. So, that one is off the list too.
Which leaves: The class system of England.