Fill in the gaps

Human population expansion and the effects of hunting are threatening many ... to such an extent that they are almost ... . In order to ... them, many animals are kept in ... in zoos and safari parks. The idea is that when animals are able to ... in safety, their numbers will increase enough so that some can be ... into their ... habitats. Some extreme animal rights activists, however, believe that it is better to allow a species to become extinct than to ... them in a prisonlike zoo.