Moe has a big exam tomorrow. He considered studying this evening, but decided to hang out with Curly instead. If neither activity involves any explicit costs, and Moe always chooses rationally, it mus
A. Moe gets more benefit from spending time with Curly than from studying
B. Moe gets less benefit from spending time with Curly than from studying
C. the opportunity cost of studying is less than the value Moe gets from spending time with Curly
D. the opportunity cost of studying is greater than the value Moe gets from spending time with Curly
Positive economic principles are those that（）
A. indicate how people should behave
B. are always correct
C. are influenced by political ideology
D. predict how people will behave
Normative economic principles are concerned with how people_make decisions while positive economic principles are concerned with how people_make decisions（）
A. in power; in ordinary life
B. do; should
C. should; do
D. in ordinary life; in power
The cost-benefit model used by economists is（）
A. useful because most people follow it most of the time
B. useful because everyone follows it all of the time
C. unrealistic because it is too detailed and specific to apply to most situations
D. unrealistic because everyone can think of times when he or she violated the principle
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