[单项选择]Zoos have become an important site for the preservation and protection of wildlife resources, (62) those species that are endangered. (63) , many zoos displayed live animals for public entertainment. Presently some zoos have become scientific and educational institutions that have (64) to the understanding and conservation of wild animal populations. Among the (65) facing modern zoos are the cost of upgrading old facilities, the struggle to obtain sufficient operating funds, (66) the need to attract more visitors to new and entertaining exhibits.
Many older zoos in American cities have (67) renovation (翻新) during the last decades of the twentieth century. Among the recent (68) in zoo improvement is the construction of new enclosures that (69) natural habitats (栖息地). The replacement of traditional steel bars and concrete floors (70) appropriately designed surroundings improves visitor appreciation of th