A、The city can be a lonely place. B、life in the West can be very dangerous. C、People in the West are fond of animals. D、The dog

When you take a walk in any of the cities in the West, you often see a lot of people walking dogs. It is still true that a dog is the most useful and faithful animal in the world, but the reasons why people keep a dog have changed. [22]In the old days people used to train dogs to protect themselves against attacks by other beasts. And later they came to realize that [23]a dog was not only useful for protection but willing to obey his master. For example, when people used dogs for hunting, the dogs would not eat what was caught without permission. But now people in the city need not protect themselves against attacks of animals. Why do they keep dogs, then? Some people keep dogs to protect themselves from robbery. [24]But the most important reason is for companionship. For a child, a dog is his best friend when he has no friends to play with. For young couples, a dog is their child when they have no children. For old couples, a dog is also their child when their real children have grown up. So the main reason why people keep dogs has [25]changed from protection to friendship.
22. According to the passage, what were dogs trained for in the past?
23. Why were dogs used for hunting?
24. What is the most important reason for people in the city to keep dogs now?
25. What is the main idea of this passage?