【单选题】

Zoos have become an important site for the preservation and protection of wildlife resources, (61) those species that are endangereD、 (62) , many zoos displayed live animals for public entertainment. Presently some zoos have become scientific and educational (63) that have contributed to the understanding and conservation of wild animal populations. (64) the challenges facing modern zoos are the cost of upgrading old facilities, the struggle to obtain 65 operating funds, and the need to attract more visitors to new and entertaining exhibits.

Many (66) zoos inAmerican cities have undergone renovation (翻新) during the last decades of the twentieth century.Among the recent trends in zoo (67) is the construction of new enclosures that resemble natural habitats (栖息地). The replacement of traditional steel bars and concrete floors (68) appropriately designed surroundings improves visitor appreciation of the animals. Such renovations may (69) stress on animals and allow them to interact with one another more naturally.
Several major zoos conduct captive propagation programs.A、captive propagation program includes the breeding of (70) zoo or wild animals to obtain offspring, usually for release to (71) or for transfer to other zoos.Captive breeding is one method of 72 some species from extinction.
Zoos have expanded and improved public education programs also, with education departments that develop programs (73) zoo exhibits. Public activities include in-school programs, zoos tours, special events, and websites. The Zoological Society of New York, for example, conducted a major project with a WesternAfrican government to monitor an elephant herd (74) it moved throughout its range.
The importance of zoos will increase as natural habitats are diminishing. Through will their efforts (75) conservation, education, and environmental advocacy, zoos continue to play a critical role in wildlife preservation throughout the worlD、
A．By that time
By the time
C．At one time
D．At that time