If I scratch your back and you scratch mine, then we’re both better off as a result—so goes the principle of reciprocity. As humans, we are familiar with the concept, whether it is by buying rounds of drinks or expelling diplomats. But do animals also help those who help them? The answer may be yes. A paper by Dolivo and Taborsky shows that Norway rats will only give as good as they get.
In their laboratory, Dolivo and Taborsky first trained rats to pull a stick that provided a food item within the reach of a rat in a neighboring cage separated from them by wire mesh(铁丝网)．
They then introduced a further treatment in which an experimental rat was placed in a cage with other caged rats on either side. On one side the rat pulled a stick that provided pieces of carrot to the rat in the central cage, while the other pulled a stick that produced banana pieces.
In the following trials the focal rat (the one in the central cage) had the opportunity to repay the other rats using the same stick tool to deliver food items.
Now, the rats had typically turned their noses up at the carrot and showed a strong preference for the more desirable banana. On the basis that the banana－providing rat should be therefore remembered as the superior partner, the authors predicted that in the test phase(阶段) the focal rat would more readily provide help for banana－offering rats than for carrot－offering rats. This proved to be the case: the rats that had provided better help in the past received greater rewards—it seemed that they were behaving reciprocally.
Dolivo and Taborsky’s experiments show that rats can recall the quality of help provided and by which rat, and adjust their behavior so as to invest more time and energy in helping those that helped them. It is apparent that we shouldn’t undervalue the ability of animals to engage in reciprocity.
4．What does the underlined word “reciprocity” probably refer to?
A．The act of being kind to other people.
B．A cooperative exchange of favors.
C．A positive attitude to everything.
D．The quality of being generous.
5．What would happen if a rat pulled the stick?
A．It would find some food in its own cage.
B．Other rats would be able to enter its cage.
C．Another rat in another cage would get food.
D．It would be able to enter a neighboring cage.
6．Which got more benefit from the focal rat?
A．The rats that preferred carrot pieces.
B．The rats that preferred banana pieces.
C．The rats that had provided carrot pieces.
D．The rats that had provided banana pieces.
7．Which of the following might Dolivo and Taborsky agree with?
A．Some animals may return others’ help.
B．Norway rats have very poor memories.
C．It is hard to explain the ability of animals.
D．Rats’ behavior is very uncommon.
阅读理解B
【解题导语】　本文是一篇说明文。文章详细介绍了Dolivo和Taborsky用挪威老鼠做实验得出结论的过程。实验的结果告诉人们，我们不应该低估动物的互惠能力。
4．B　解析：词义猜测题。根据第一段第一句中的“If I scratch your back and you scratch mine, then we’re both better off as a result”可知，如果两个人互相抓背，则两个人都能得到好处；由此可推知，reciprocity意为“互惠”，故B项正确。
5．C　解析：推理判断题。根据第二段的内容和第三段尾句“On one side the rat pulled a stick that provided pieces of carrot to the rat in the central cage, while the other pulled a stick that produced banana pieces”可推知，如果一只老鼠拉棍子，则另一个笼子里的老鼠会吃到食物，故C项正确。
6．D　解析：细节理解题。根据倒数第二段的内容尤其是“the rats that had provided better help in the past received greater rewards”可知，提供香蕉片的老鼠会得到更多的回报，故D项正确。
7．A　解析：推理判断题。根据尾段第一句可知，Dolivo和Taborsky的实验表明，老鼠能够回忆起谁提供的帮助和帮助的质量，并调整它们的行为，从而投入更多的时间和精力去帮助那些帮助过它们的同类；由此可推知，动物会回报帮助过它们的对象，故A项正确。