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.

    You probably know that frogs hop (双足跳). But did you know that there's a small frog in the Pacific Northwest that belly flops (肚子先着水)? It's called a tailed frog.

    Dr. Rick Eisner, who has been studying tailed frogs for the past few years, says, "I've looked at thousands of jumps and have never seen them land on their feet like other frogs." Most of the time, tailed frogs land on their stomachs and then bring their back legs in to prepare for another jump.

    Eisner first noticed these frogs because of the way they swim. Other frogs kick both of their back legs at the same time. But when a tailed frog swims, it pushes first with one leg and then the other.

    To try to find out why tailed frogs bellyflop, Eisner and other scientists collected and filmed different kinds of frogs. They found that all of the frogs start their jumps the same way: They hold out their legs. The change comes in the landing. Tailed frogs can't move their back legs as quickly as other frogs do. Maybe they don't need to. Tailed frogs live around water and quickly jump into the water to escape danger.

    Early frogs developed around watery areas and could jump quickly into the water to escape danger. Scientists think those frogs blended in with (与…融合在一起) the green plants on the side of the rocky rivers, just like today's tailed frogs. "I would guess that other animals would have problems detecting them," explains Eisner. When other animals find those early frogs, the frogs could jump into the river. They didn't need to continue hopping.

    Tailed frogs and other kinds of frogs went their own ways about 200 million years ago. Tailed frogs stayed by rivers. Other kinds of frogs moved to places where new hopping skills allowed them to survive.

They learned this from .

The animals there are lovely, but the number of them is decreasing year by year. (宾语从句)

The animals there are lovely, but the number of them is decreasing year by year. (主语从句)