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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____.