A. To outline contrasting types of economic systems. B. To explain the science of economics. C. To argue for the superiority of one economic system. D. To compare barter and money exchange markets. 参考答案:A 答案解析:[解析] 本题是一道归纳题。这道题要求考生通读全文,归纳出本文的中心大意。本文介绍了三种不同的经济体制,并客观地进行了对比,所以答案为A)。