L3：
1. What is the main purpose of the lecture?
To compare the behaviors of three different bear species
To examine changes to the habitat in which polar bears live
To discuss recent insights into polar bear evolution
To illustrate a new method of DNA analysis used in climate studies
2. Why did the researchers that the professor mentions use mitochondrial DNA for testing instead of nuclear DNA?
Mitochondrial DNA has a more stable structure than nuclear DNA has.
Mitochondrial DNA has a shape that is more easily identifiable than that of nuclear DNA.
Mitochondrial DNA is present in larger quantities in cells than nuclear DNA.
Mitochondrial DNA analysis is a better-understood research tool than nuclear DNA analysis
3. What point does the professor make about brown bears?
They now compare with polar bears for food- and territory.
They are the ancestors of polar bears.
They face the same environmental threat as polar bears.
Their jawbones can be easily distinguished from those of polar bears.
4. According to the professor, what do researchers believe about the Svalbard islands?
Polar bears first came into existence as a species on the islands.
The separate islands were once joined together in a single large landmass.
Interbreeding between polar bears and a species of brown bear occurred on the islands. The islands provided a refuge for polar bears during an ancient warming period.
5. What does the professor imply when she discusses the current warming period?
The consequences of the current warming period will not be as serious as most
scientists believe.
The current warming period is progressing more slowly than previous warming periods.
Arctic temperatures today are similar to temperatures during previous warming periods.
The fast pace of the current warming period will threaten polar bears’ long-term survival.
6. Why does the professor imply when she says this:(无录音)
The size of the grizzly bear population will soon stabilize.
The future of the polar bear as a distinct species might be at risk.
Hybridization has already diminished the polar bear population within a short period of time.
Hybrid species do not adapt well to sudden changes in the environment.
