发布时间：2017-06-28 来源：新东方在线 发布人：young
One of the world's last four remaining northern white rhinos has died in a zoo in the United States.
The condition of Nola, a 41-year-old female, had deteriorated after surgery and she was put down on Sunday.
Nola had been a popular attraction at the San Diego Zoo Safari Park since 1989.
The remaining three northern white rhinos - all elderly - are kept closely guarded at the Ol Pejeta Conservancy in Kenya.
Nola underwent surgery on 13 November to drain a hip abscess. However, her health deteriorated a week ago and worsened again over the weekend and it was decided she should be put down.
The northern white rhino population was decimated by poachers seeking their prized horns, and was declared extinct in the wild in 2008.
San Diego zoo has recently brought in six southern white rhinos, hoping to use them as surrogate mothers for northern white rhino embryos.
There are about 20,000 southern white rhinos in the world, but studies are still taking place to determine whether the subspecies are genetically similar enough for the surrogacy to work.
Zoo researchers say that, if successful, the programme could see a northern white rhino calf born within 10 to 17 years.