阅读理解 Economists often like to speak of Homo economicus—rational economic man. In practice, human economic behaviour is not quite as rational as the relentless logic of theoretical economics suggests it ought to be. When buying things in a straight exchange of money for goods, people often respond to changes in price in exactly the way that theoretical economics predicts. But when faced with an exchange whose outcome is predictable only on average, most people prefer to avoid the risk of making a loss than to take the chance of making a gain in circumstances when the average expected outcome of the two actions would be the same.
There has been a lot of discussion about this discrepancy in the economic literature—in particular, about whether it is the product of cultural experience or is a reflection of a deeper biological phenomenon. So Keith Chen, of the Yale School of Management, and his colleagues decided to investigate its evolutionary past. They reasoned that if they could find similar behavior in another species of primate(none of which has yet invented a cash economy)this would suggest that loss-aversion evolved in a common ancestor. They chose the capuchin monkey, Cebus apella, a South American species often used for behavioral experiments.
First, the researchers had to introduce their monkeys to the idea of a cash economy. They did this by giving them small metal discs while showing them food. The monkeys quickly learned that humans valued these inedible discs so much that they were willing to trade them for scrumptious pieces of apple, grapes and jelly. Preliminary experiments established the amount of apple that was valued as much as either a grape or a cube of jelly, and set the price accordingly, at one disc per food item. The monkeys were then given 12 discs and allowed to trade them one at a time for whichever foodstuff they preferred.
Once the price had been established, though, it was changed. The size of the apple portions was doubled, effectively halving the price of apple. At the same time, the number of discs a monkey was given to spend fell from 12 to nine. The result was that apple consumption went up in exactly the way that price theory(as applied to humans)would predict. Indeed, averaged over the course of ten sessions it was within 1% of the theory's prediction. One up to Cebus economicus.
The experimenters then began to test their animals' risk aversion. They did this by offering them three different trading regimes in succession. Each required choosing between the wares of two experimental "salesmen". In the first regime one salesman offered one piece of apple for a disc, while the other offered two. However, half the time the second salesman only handed over one piece. Despite this deception, the monkeys quickly worked out that the second salesman offered the better overall deal, and came to prefer him.

【正确答案】 D

【答案解析】属细节题。根据题干中the idea of a cash economy回到原文第三段第二句。“did this”指的就是introduce their monkeys to the idea of a cash economy，他们给猴子们一些小金属圆片，同时向它们展示食物。通过这种办法给猴子的大脑里引入现金交易的概念，所以D为正确答案。A中的told没有事实依据。B项说如果猴子给研究人员食物，就能得到金属圆片，这明显不对，应该是猴子们用金属圆片买研究人员手里的食物。文章中没有明确表明三种不同食物的不同价格，所以排除C。