1 . From the moa in New Zealand to the dodo in Mauritius (both of these two flightless birds have died out), the arrival of humans has often spelled extinction for tasty but previously isolated animals. Many scientists had assumed that the woolly rhinos (长毛犀牛) suffered the same thing. But Love Dalén, a professor at the Centre for Palaeogenetics in Stockholm. and Edana Lord, one of Dr Dalén's PhD students, are not so sure.

Until recently, information on the story of this great ice-age animal had been limited to the fossilized bones (骨骼化石). In the past couple of decades, however, scientists have learned to use a richer source of information： ancient genomes (基因组). By itself, DNA breaks down quickly, attacked by water and sunlight. But DNA covered in bones and teeth can survive longer, especially if those bones and teeth are themselves in permanent frozen land. It was this sort of DNA that enabled Dr Dalén and Ms Lord to investigate the woolly rhinos' disappearance.

Working with a team of colleagues, the researchers obtained DNA from 12 woolly rhino bones collected from permafrost in Siberia. Analyzing the genetic diversity of the bones, the researchers found that rather than declining as humans arrived, the population of rhinos remained stable from 29,000 years ago to 18,500 years ago, a few thousand years before they died out. Perhaps the people who met the animals found them distasteful. Or perhaps the rhinos were simply too dangerous to hunt with their simple weapons.

On the other hand, the animals' decline lines up suggestively with a rapid period of global warming that began around 14,700 years ago. The researchers argue that this was the more likely cause of the animals' disappearance. This time, it seems, it was Mother Nature who did it.

1. What probably caused the extinction of the moa and the dodo?

A．Human activity.	B．Geographical disasters.
C．Lack of food.	D．Climate change.

2. How did the team carry out their investigation?

A．By testing DNA itself.

B．By collecting fossilized bones.

C．By analyzing ancient genomes.

D．By studying the permanent frozen land.

3. What happened to the rhinos after man arrived according to the text?

A．They disappeared quickly.

B．They decreased in numbers.

C．They were hunted as foo

D．They co-existed with humans long

4. Which can be a suitable title for the text?

A．Mother Nature Is Actually the Killer

B．What Killed Woolly Rhinos?

C．Woolly Rhino Bones Were Found in Siberia

D．What Happened to Woolly Rhinos?