A、Fewer colors. B、Smaller size. C、Fewer frames per second. D、No sound. C

Domestic dogs can perceive images on television similarly to the way we do, and they are intelligent enough to recognize onscreen images of animals as they would in real life—even animals they’ve never seen before—and to recognize TV dog sounds, like barking. A 2013 study published in the journal Animal Cognition showed that dogs could identify images of other dogs among pictures of humans and other animals, using their visual sense alone.
    However, there are some differences between ourselves and man’s best friend—for one, dogs’ eyes register images more quickly than ours do. So older television sets, which show fewer frames per second than modern televisions, would appear to a dog to be flickering like a "1920s movie" , said Nicholas Dodman, a veterinary behaviorist at Tufts University, in Massachusetts. Dogs can see a range of two primary colors, yellow and blue. Human can recognize three primary colors, so we see the full range of colors, according to Binghamton University’s Ask a Scientist web page.
    DogTV, an HDTV cable channel designed for dogs, interests canines because HDTV has a much higher number of frames per second and is specially colored to accommodate dogs’ vision, said Dodman, who is the channel’s chief scientist. DogTV has modes for relaxation, which shows images like dogs chilling out in a grassy field: stimulation, which depicts scenes like dogs surfing in southern California: and exposure which shows things like a dog reacting to a ringing doorbell and obeying commands to adapt them to such situations at home.
23. What makes older television sets unsuitable for dogs to watch?
24. What primary colors can dogs see?
25. What kind of programs are shown on DogTV?