問題：Assume that two small countries, A and B, produce two commodities, X and Y, and that there are no transport costs.
　　One unit of resource utilized in Country A produces 40 units of X or 80 units of Y. One unit of resource utilised in Country B produces 15 units of X or 25 units of Y.
　　According to the law of comparative advantage, which one of the following statements is true?
　　A. Country A has a comparative advantage over Country B in producing Y
　　B. Country A has an absolute advantage over B in producing both products and so will not trade
　　C. Country B has a comparative advantage over Country A in producing Y
　　D. Country A has a comparative advantage over Country B in producing X
　　答案：The correct answer is: Country A has a comparative advantage over Country B in producing Y.
　　Country A is 3.2 times (80/25) more efficient than Country B at producing Y; but 2.67 (40/15) times as efficient at producing X.