A、To teach dogs to recognize facial expressions. B、To teach dogs to memorize things. C、To teach dogs to dance. D、To teach dogs t

Dogs are very mindful of sound. When dog owners shout or speak in a strong, harsh voice, dogs often act guilty and quietly move away from the area. Recently, researchers found that dogs can look at our faces, and tell the difference between a smile and a frown. The animals were able to recognize a look of approval from one of disapproval.
    Researchers at the University of Veterinary Medicine, Vienna performed a series of experiments.
    They taught dogs to recognize facial expressions. They showed the dogs two pictures of either the upper or lower half of a persons face. On one picture, the person looked happy. The other appeared angry. The dogs were then shown images of the eyes or mouths of people they had never seen before. They were also shown the left half of the faces used in training.
    Corsin Muller led the study. ’’We were essentially speaking, do they realize that smiling eyes have the same meaning as a smiling mouth, or angry eyes have the same meaning as an angry mouth? And it turned out that they really did perform very well in these probe trials. Once they had learned the initial discrimination, they could spontaneously, immediately choose the correct one also in the probe trials with the normal stimuli. ’’Once the dogs learned to recognize which image was happy or angry, they could easily identify the same expressions in pictures of any face.
    Corsin Muller says future studies will try to show whether dogs can learn the meaning of facial expressions—for example, whether a frown shows that someone is angry. ’’What we can say with our study is that they can discriminate them, that they can tell these ones are different. But what we cannot be sure of at this point is what exact meaning they are associating with these different expressions. ’’’’Seems of course likely that they would associate some positive meaning with the smiley face and they would associate some rather negative meaning with the angry face. But what exactly they are associating with these expressions we cannot know at this point. ’’
    In the experiments, researchers found the dogs were slower to link a reward, or prize, with recognition of the angry face. This suggested that dogs had an idea people with angry faces were best avoided. Corsin Muller says canine investigators are also interested in finding out whether wild wolves can be trained to recognize human facial expressions. The researchers’ findings were published in the journal Current Biology. They provide the first solid evidence that humans are not the only species that can read the body language of another species.
23. What does a dog do when its owner shouts at it?
24. What is the purpose of the experiments made at the University of Veterinary Medicine?
25 . What is the significance of the researcher’s findings?