Modern zoos are very different from zoos built fifty years ago. At that time, zoos were places ___1___people could see animals from many parts of the world. The animals lived in _____2___with iron bars. The cages were easy to keep clean.__ 3___, for the animals, the cages were small and impossible to hide in. Although the zoo ____4____ took good care of them, many of the ____5____ did not feel comfortable, and they often became ____6____.
In modern zoos, people can see animals in more _____7___ conditions. The animals are given more freedom in larger places ____8____ they can live more freely as they would in _____9___. Even the appearance of zoos has changed. Trees and grass grow in the cages, and water flows____10____ the places that the animals live in. There are few bars,____ 11____ there is often a deep ditch(沟), filled with _____12___, which surrounds a space where several_____13___ of animals live together as they would naturally. In an American zoo, the visitor can walk ____14____ a huge special cage that is filled with trees, some small animals and many birds. And it is large enough for all the birds to live ____15____.In a zoo in New York, because of special night ____16____, people can observe certain animals that are ___17_____ only at night when most zoos
