Wildlife conservationists in Kenya are trying to save a rare kind of rhinoceros .Somanynorthernwhiterhinoshavebeenhuntedandkilled that they are almost dying out. There were only five northern white rhinos left. So the workers hoped they could save the rhinos by helping them produce young. Three northern white rhinos lived at The Ol Pejeta Conservancy in Kenya. Workers with military weapons guarded the rhinos as they walked, played and ate over a large area of natural grass and trees. The three rhinos were brought to the conservancy in 2009 from a zoo in the Czech Republic. Workers hoped they would have a better chance of survival in a more natural habitat. But breeding has not been as successful as they had hoped. And the number of northern white rhinos continues to decrease. One of the rhinos at the conservancy died in October. Another died at a zoo in the US city of San Diego, California earlier this month. The San Diego zoo still has one northern white rhino left. The zoo in the Czech Republic also has one. The last wild northern white rhinos were hunted and killed during conflicts in the Democratic Republic of Congo over the past ten years. Rhinos are killed because many people in Asia want the animals'horns .They believe the horns will help with medical problems. But researchers say there is no medicine in the horn, just a kind of hair. The last male northern white rhino is 41 years old. He has been unsuccessful in producing young with a female rhino. So conservationists will use artificial methods to make a young female become pregnant. If that is not successful, they will try to fertilize a northern rhino egg and put it into a southern white rhino, who will act as a surrogate  mother. The last solution would be cross-breeding between the northern and southern white rhino species. If cross-breeding is successful, there is hope that some part of the northern white rhino species may still live on. People hunted and killed rhinos because  _  .
they wanted to get rhinos' horns for medical use rhinos ate natural grass and trees on their farmland get rid of the threat of rhinos from their life they wanted to do researches on producing young for rhinos
Question: Wildlife conservationists in Kenya are trying to save a rare kind of rhinoceros .Somanynorthernwhiterhinoshavebeenhuntedandkilled that they are almost dying out. There were only five northern white rhinos left. So the workers hoped they could save the rhinos by helping them produce young. Three northern white rhinos lived at The Ol Pejeta Conservancy in Kenya. Workers with military weapons guarded the rhinos as they walked, played and ate over a large area of natural grass and trees. The three rhinos were brought to the conservancy in 2009 from a zoo in the Czech Republic. Workers hoped they would have a better chance of survival in a more natural habitat. But breeding has not been as successful as they had hoped. And the number of northern white rhinos continues to decrease. One of the rhinos at the conservancy died in October. Another died at a zoo in the US city of San Diego, California earlier this month. The San Diego zoo still has one northern white rhino left. The zoo in the Czech Republic also has one. The last wild northern white rhinos were hunted and killed during conflicts in the Democratic Republic of Congo over the past ten years. Rhinos are killed because many people in Asia want the animals'horns .They believe the horns will help with medical problems. But researchers say there is no medicine in the horn, just a kind of hair. The last male northern white rhino is 41 years old. He has been unsuccessful in producing young with a female rhino. So conservationists will use artificial methods to make a young female become pregnant. If that is not successful, they will try to fertilize a northern rhino egg and put it into a southern white rhino, who will act as a surrogate  mother. The last solution would be cross-breeding between the northern and southern white rhino species. If cross-breeding is successful, there is hope that some part of the northern white rhino species may still live on. People hunted and killed rhinos because  _  .
A. they wanted to get rhinos' horns for medical use
B. rhinos ate natural grass and trees on their farmland
C. get rid of the threat of rhinos from their life
D. they wanted to do researches on producing young for rhinos
Answer: