But in the park, park rangers did that in the 1920s, and then 60 years later they had to bring them back, because the elk numbers had gotten out of control.
20世纪90年代， 公园管理员们把狼杀光了， 60年后，他们又得送些狼进公园里， 因为没有了狼，公园里的麋鹿 数量疯长不可控了。