阅读短文，从每题所给的A、B、C和D四个选项中，选出最佳选项。
Nola is a 41-year-old northern white rhino (犀牛) that lives at the San
Diego Zoo Safari Park in Escondido, California. She is one of only four remaining
northern white rhinos in the world, and the only one in the western part of the
earth. The other three live in Kenya (肯尼亚).
Rhinos have lived on earth for more than 40 million years, but they are now
at the risk of dying out. Hunters illegally hunt rhinos for their horns (角), which are used for art,
jewelry, and decorations. They sell the horns for thousands of dollars per pound,
though it is not allowed by law. Rhino horns are also prized as a key part in traditional
medicine, even though scientific tests have proven that the horns cannot cure illnesses.
Experts say that every eight hours, one rhino will be hunted.
Scientists are trying to find ways to prevent rhinos from dying out. In 1975,
the San Diego Zoo Institute for Conservation Research started the Frozen Zoo, a
program through which researchers have collected cell samples (细胞样品) from more than 8,
000 different animal species until now, including the northern white rhino. Scientists
hope that by studying the rhino cells, they will gain greater understanding of the
species, and will find ways to increase its number.
Jeanne Loring works with the Frozen Zoo. Loring's research focuses on pluripotent
stem cells, which are cells that can renew and become any cell type. Coloring's
lab at TSRI is working together with scientist Oliver Ryder of the San Diego Zoo
to use plenipotentiary stem cells to try to increase the number of the northern
white rhino. Loring said the goal is to start producing new rhinos through this
method over the next couple of years.
