A、By observing their facial features carefully. B、By focusing on a particular body movement. C、By taking in their facial express

Dogs, man’s best friends, have a clear strategy for dealing with angry owners—they look away.
    (19) New research shows that dogs limit their eye contact with angry humans. The scientists suggest this may be an attempt to calm humans down. This behavior may have evolved as dogs gradually learned they could benefit from avoiding conflicts with humans.
    To conduct the tests, the University of Helsinki researchers trained 31 dogs to rest in front of a video screen. Facial photos of dogs and humans were displayed on the screen for 1.5 seconds. They showed threatening, pleasant and neutral expressions. Nearby cameras tracked the dogs’ eye movements.
    Dogs in the study looked most at the eyes of humans and other dogs to sense their emotions. (20) When dogs looked at expressions of angry dogs, their eyes rested more on the mouth, perhaps to interpret the threatening expressions. And when looking at angry humans, they tended to turn away their gaze.
    Dogs may have learned to detect threat signs from humans and respond by trying to make peace, according to researcher Sanni Somppi. Avoiding conflicts may have helped dogs develop better bonds with humans.
     (21) The researchers also note that dogs scan faces as a whole to sense how people are feeling. Instead of focusing on a given feature, they suggest this indicates that dogs aren’t sensing emotions from a single feature, but piecing together information from all facial features just as humans do.
Question 19 to 21 are based on the passage you have just heard.
19. What do dogs do when they are faced with angry humans?
20. What does a dog do when it sees the expressions of angry dogs?
21. How does a dog sense? people’s? feelings?