Passage Four

　　We all know that people sometimes change their behavior when someone is looking their way. Now, a new study reported online on April 2nd in Current Biology shows that jackdaws —birds related to crows with eyes that appear similar to human eyes — can do the same.

　　“Jackdaws seem to recognize the eye’s role in visual perception, or at the very least they are extremely sensitive to the way that human eyes are oriented,” said Auguste von Bayern, formerly of the University of Cambridge and now at the University of Oxford.

　　When presented with a preferred food, hand-raised jackdaws took significantly longer to retrieve the reward when a person was directing his eyes towards the food than when he was looking away, according to the research team led by Nathan Emery of the University of Cambridge. The birds hesitated only when the person in question was unfamiliar and thus potentially threatening.

　　In addition, the birds were able to interpret human communicative gestures, such as gaze alternation and pointing to help them find hidden food, they found. The birds were unsuccessful in using static cues, including eye gaze or head orientation, in that context.

　　Unlike most birds, jackdaws’ eyes have a dark pupil surrounded by a silvery white iris. The researchers said they believe jackdaws are probably sensitive to human eyes because, as in humans, eyes are an important means of communication for them. The hand-raised birds examined in the study may be even better than wild jackdaws at attending to human gaze and responding to the gestures of the people who have raised them.

　　The findings are particularly notable given that most other species investigated so far, including our closest relatives the chimpanzee and “man’s best friend,” the dog, are not particularly sensitive to eye orientation and eye gaze, von Bayern said. Rather, she continued, chimps and dogs seem to rely on other cues such as head or body orientation in determining the looking direction of others and do not appear to appreciate the eyes as the visual organs. The results suggest that birds may deserve more respect for their mental abilities.

　　Questions 16-20 are based on Passage Four.

　　16. According to the report, when does a hand-raised jackdaw hesitate to take a preferred food?

　　A. When the feeder is looking away from the food.

　　B. When the feeder is unfamiliar to the bird.

　　C. When the. feeder holds the food in his hand.

　　D. When the feeder is looking at the food.

　　17.According to the researchers，jackdaws can notice human eye orientation probably because ______.

　　A.1ike humans，they also use eyes to communicate

　　B.they are far more intelligent than other birds

　　C.they are mostly hand-raised by humans

　　D.their eyes also have a dark pupil

　　18.According to the 4th paragraph，jackdaws are good at interpreting all of the following cues EXCEPT ______.

　　A.alternating one’s gaze to another direction

　　B.pointing to where the food is hidden

　　C.keeping a long gaze at one direction

　　D.directing one’s eyes towards the food

　　19.Why does the author refer to chimpanzees and dogs in the last paragraph?

　　A.To suggest that they are much better at interpreting gaze alternation.

　　B.To illustrate how unique jackdaws are in being able to notice gaze orientation.

　　C.To make clear that they rely on other means in determining people’s intention.

　　D.To show that they communicate more frequently with humans than jackdaws.

　　20.What does the research finding suggest?

　　A.We know embarrassingly less about birds than we assume.

　　B.The closer we communicate with animals，the better we understand them.

　　C.Not all jackdaws are good at attending to human gaze.

　　D.We may have underestimated jackdaws’ mental abilities.