What kinds of questions does economics address?What are the principles of how people make decisions?What are the principles of how people interact?What are the principles of how the economy as a whole works?What are economists’ two roles? How do they differ?What are models? How do economists use them?What are the elements of the Circular-Flow Diagram? What concepts does the diagram illustrate?How is the Production Possibilities Frontier related to opportunity cost? What other concepts does it illustrate?What is the difference between microeconomics and macroeconomics? Between positive and normative?