【正确答案】 B

【答案解析】[听力原文]
A market can be seen as a set of economic forces called supply and demand. Supply forces tend to bring goods and services into production. Demand forces tend to result in consumption of those goods and services. Supply and demand forces interact to form a price. Since markets play a large role in our economy, we say we have a market economy. A market economy is an economic system in which prices determine how resources will be used and how products will be distributed.
Price is the quantity of money (or other products) paid in exchange for something else. The current price of something, then, influences how much of it is produced and how much of it is consumed. A producer of several different things is likely to produce more of those that bring relatively higher prices. So, if a consumer"s buying power is limited, he or she is likely to compare prices of different things before buying.
In nearly all economies, money is used as a medium of exchange. That is, the prices of all things are expressed in terms of a common money unit, such as the US dollar. This makes exchanges and product choices easier.
In a market economy, it is prices that mainly determine what goods and services to produce, how much of each to produce, how to produce them, and who will get them. A market economy, therefore, can also be called a price system.