A、They should not be frightened by wild horses. B、They should not be disturbed by other noises. C、They should understand the hor

Animals perform many useful and entertaining jobs. Dogs are particularly valuable in guiding the blind, protecting property, finding lost people, and hunting criminals. Horses are used in guarding herds, carrying men in lands when there are no roads and helping farmers work their lands. Pigeons have long been used to carry messages.
    Dogs are extremely useful as companions for blind people. When a dog has been properly trained, he will always lead its blind master in the right direction and keep him out of danger. For example, seeing-eye dogs learn never to cross a busy road when cars are coming, even if their masters command them to do so.
    Horses are also able to learn a lot of things. Horses that are used for guard or police duty must learn never to be frightened of noises, traffic and other disturbances. Therefore it is necessary for those who train them to be very patient and understanding.
    Pigeons have a natural instinct to return home, even if they are far away and the trip is very hard and dangerous. Men utilize this instinct to send messages on small pieces of paper which are fastened to the pigeon’s backs or legs. In wartime, pigeons have been known to fly as fast as 75 miles an hour and to cover a distance of 500 to 600 miles.
    People have realized that although animals may not have the intelligence as human beings, they are smart enough to learn many things.
Questions 26 to 28 are based on the passage you have just heard.
26. What is the passage mainly about?
27. What can be inferred from the passage?
28. What is required for trainers of horses used for guard?