2. 考研
  3. Zoos have become an important site for the preservation and protection of wildlife resources,【C1】______those species that are en

Zoos have become an important site for the preservation and protection of wildlife resources,【C1】______those species that are en

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问题     Zoos have become an important site for the preservation and protection of wildlife resources,【C1】______those species that are endangered【C2】______, many zoos displayed live animals for public entertainment. Presently some zoos have become scientific and educational【C3】______that have contributed to the understanding and conservation of wild animal populations【C4】______the challenges facing modern zoos are the cost of upgrading old facilities, the struggle to obtain【C5】______operating funds, and the need to attract more visitors to new and entertaining exhibits.
    Many【C6】______zoos in American cities have undergone renovation (翻新) during the last decades of the twentieth century. Among the recent trends in zoo【C7】______is the construction if new enclosures that resemble natural habitats (栖息地) . The replacement of traditional steel bars and concrete floors【C8】______appropriately designed surroundings improve visitor appreciation of the animals. Such renovation may【C9】______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【C10】______zoo or wild animals to obtain offspring, usually for release to 【C11】______or for transfer to other zoos. Captive breeding is one method of【C12】______some species from extinction.
    Zoos have expanded and improved public education programs also, with education departments that develop programs【C13】______zoo exhibits. Pubic activities include in-school programs, zoo tours, special events, and websites. The Zoological Society of New York, for example, conducted a major project with a Western African government to monitor an elephant herd【C14】______ito moved throughout its range.
    The importance of zoos will increase as natural habitats are diminishing. Through their efforts【C15】______conservation, education, and environmental advocacy, zoos will continue to play a critical role in wildlife preservation throughout the world.
【C2】
选项 A、By that time
B、By the time
C、At that time
D、At one time
答案D
解析 At one time曾经，一度。表示过去曾经做过某事，从后面句子中的displayed一词判断，是在描述过去的事情。答案应选D。
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