Dogs have an understanding of fair play and become angry if they feel that another dog is getting a better deal, a new study has found.
The study looked at how dogs react when a companion is rewarded for the same trick in an unequal way. Friederike Range, a famous researcher, and her colleagues did a series of experiments with dogs who knew how to respond to the command “give the paw”. The dogs were normally happy to repeatedly give the paw, whether they got a reward or not.
But that changed if they saw that another dog was being rewarded with a piece of food, while they received nothing. The dogs hesitated significantly longer when obeying the command to give the paw. Eventually, the unrewarded dogs stopped cooperating.
Researchers always assumed that only humans pay close attention to unfairness. That changed in 2003 when Frans De Waal, a professor of psychology, and a colleague named Sarah Brosnan did a survey on monkeys. Monkeys had to hand a small rock to researchers to get a piece of cucumber(黄瓜) in return. However, the monkeys would suddenly become angry when receiving the piece of cucumber if they saw another monkey receive a more delicious reward, such as a grape, for doing the same job. The monkey that got the cucumber would eventually throw away the food and the rock, and would later just stop performing.
In that experiment, the monkeys considered the fairness of two different types of payment, but when Range and her colleagues did a similar study with their trained dogs, testing to see if dogs would become upset if they only got bread when other dogs received sausage, they found that dogs did not make that kind of subtle (细微的) distinction. As long as the dogs got some kind of food payment, even if it wasn’t the most delicious kind, they would play along.
The dogs refused to give their paws when they _____________________.

A．were given too much reward

B．realized they received less food

C．found another dog was given nothing

D．felt they were being treated unequally

The underlined word “that” in Paragraph 3 probably refers to “__________________”.

A．the dogs obeyed the command happily

B．the dogs waited for a reward

C．the dogs hesitated to give the paw

D．the dogs stopped cooperating

The monkeys would become angry if they found _____________________.

A．they were being given the same type of food

B．another monkey did much less work

C．another monkey was offered tastier food

D．other monkeys threw food and rocks

Range finds that, compared with monkeys, dogs __________________.

A．enjoy playing interesting games with humans

B．prefer to do the same jobs as humans

C．pay little attention to the type of reward received

D．aren’t sensitive to the stimulation (刺激) of food

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