Every city has one or more zoos. For a while, people think that a zoo is no useful purpose. If I were faced with this issue, I would think that zoos are useful. In the following discussion, I would like to reason and provide evidence to support my viewpoint.The first reason is that zoos are often used as places to preserve the endangered species, such as the giant pandas and tigers. It is the conservation of animals that is the most important function of a zoo. With the advances in reproductive technologies, which assist in breeding captive animals, the zoo has become the most important place for animal conservation. Thanks to zoos, certain species of animals have been saved from extinction. Such animals are bred in captivity and when they are ready to survive in the wild, are reintroduced to their original habitat - in the rain forests of Brazil, for instance.In the second place, children can obtain direct knowledge about a variety of animals by visiting zoos. They can see what a tiger is like, hear various sounds of birds and tell one animal from another. If there is no such a place, how can they make contact with animals? They may never have a chance to see various animals even though they learn many from books. When I was a little girl, I liked animals very much, especially birds. But I could not feed them for myself, so the zoo which was located near my home was the place I went to most frequent. And I really love these places.Finally, a zoo is a place for fun. In fact, this is why it is so good at educating the public about the importance of conserving wildlife and the environment: it puts fun into education. Seeing pictures is not the same as seeing animals at close up. What makes visiting a zoo so enjoyable is our close contact with them. Therefore a zoo not only attracts many tourists from other countries, it also allows us to see, without having to leave home, big cats and exotic animals of distant countries.In summary, I believe that a zoo has some useful purposes to serve: to preserve the endangered species, to educate the public about wildlife, and for its visitors to have fun. So a zoo of course is a useful place for us and we should have them.