If you are in a town in a western country, you'll often see people walking with their dogs. It is still true that a dog is the most useful animal in the world. But the reason why one keeps a dog has changed Once upon a time, a man met a dog and wanted it to help him in the fight against other animals, and he found that the dog listened to him and did what he told him to. Later people used dogs for  hunting other animals, and the dogs didn't eat what they got until their master agreed. So dogs were used for driving sheep and guarding chicks. But now the people in the towns and cities do not need dogs to fight other animals. Of course they keep them to frighten thieves, but the most important reason is that people feel lonely in the city. For a child, a dog is his best friend when he has no friends to play with. For a young wife, a dog is her child when she doesn't have her own. For old people, a dog is also a child when their real children have grown up and left. Now people do not have to use a dog, but they keep it as a friend, just like a member of the family. In the past, people kept dogs because dogs   _  .
could fight against other animals met the people did not eat other animals helped and listened to people