阅读下面短文，在空白处填入一个适当的词，或填入括号中所给单词的正确形式。
When you take a walk in any of the cities in the West, you can see a lot of people ____(walk) with 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 ____(change). In the old days people used to train dogs to protect themselves against attacks by other beasts. And ____(late) they came ____(realize) that a dog was not only useful for protection,____ willing to obey his master. For example, when people used dogs for hunting, the dogs would not eat what was caught without ____(permit). 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. But the ____(important) reason is for companionship. For a child, ____ dog is his best friend when he has no friends to play with. For young couples, a dog is ____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 changed from protection ____ friendship.
