Economists use abstract models because（）
A. they are useful for describing general patterns of behavior
B. computers have allowed economists to develop abstract models
C. every economic situation is essentially the same, so specific details are unnecessary
D. every economic situation is unique, so it is impossible to make generalizations
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Suppose that the extra cost to Tim of a third glass of soda is zero because he’s at a restaurant that gives free refills. According to the Cost-Benefit Principle Tim should（）
A. not drink a third glass of soda
B. drink a third glass of soda if his total benefit from drinking soda is positive
C. drink a third glass of soda
D. drink a third glass of soda if the extra benefit of doing so is positive
Suppose Mary is willing to pay up to $15,000 for an used Ford pick-up truck. If she buys one for $12,000, her_would be_（）
A. benefit; $12,000
B. economic surplus; $12,000
C. cost; $15,000
D. economic surplus; $3,000
Economists believe the Cost-Benefit Principle is（）
A. a simple but useful model of how people should make choices
B. of little use to those who wish to learn how to make better decisions
C. a comprehensive description all the factors that influence people’s choices
D. an interesting intellectual exercise with little applicability to the real world
Whether studying the output of the U.S. economy or how many classes a student will take, an unifying concept is that（）
A. wants are unlimited and resources are scarce, so trade-offs have to be made
B. both wants and resources are unlimited
C. wants are limited and resources are unlimited, so trade-offs have to be made
D. wants are limited and resources are unlimited, so trade-offs are unnecessary
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