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 are closed. Some zoos have special places for visitors to ____18____ animals that live in the desert or underwater. Some other zoos have special places for animals that live in cold conditions like the ____19____ from the Arctic.
Modern zoos not only show animals for visitors, but also ____20____ and save rare animals. For this reason, fifty years from now, the grand children of today’s can still be able to enjoy watching these animals. 
1. A. that           B. where           C. which          D. there
2. A. houses         B. rooms           C. cages           D. offices
3. A.Therefore            B. However       C. So             D. Though
4. A. masters        B. managers             C. keepers         D. trainers
5 .A. workers       B. animals         C. bears           D. animals     
6. A. excited        B. angry           C. ill             D. frightened
7. A. natural        B. difficult        C. warm           D. different
8. A. so that         B. and            C. but                  D. or
9. A. forest          B. nature           C. rivers           D. the water
10. A. in           B. by             C. near             D. through
11. A. instead       B. instead of         C. and              D. or
12. A. stones        B. earth            C. oil              D. water
13. A. sorts          B. families        C. classes         D. groups
14. A. by           B. out            C. through         D. in
15. A. happily       B. naturally        C. deeply         D. hardly
16. A. moon        B. sign            C. light            D. signal
17. A. live           B. active           C. living          D. sleeping
18. A. feel           B. touch            C. watch          D. talk to
19. A. snakes       B. monkeys        C. bears           D. tigers
20. A. buy           B. keep             C. sell              D. catch