【正确答案】 B

【答案解析】[听力原文] I've mentioned how DNA has solved many mysteries in biology. And today I want to talk about how it might relate to hypothesis about the travels of the green turtle. Every winter some green turtles make a 2,000 km journey from Brazil to Ascension Island in the middle of Atlantic, where they mate and lay eggs. But the question is why do they travel so far to lay their eggs? One researcher hypothesized that there are two parts to the explanation. One is natal homing, the instinct that drives green turtles to always return to the beach where they were hatched. The second part has to do with continental drift, the theory that the positions of earth continents have changed considerably overtime. Brazil and Ascension Island were once much closer together, and continental drift drove them apart. But the turtles kept on going back to the island where they hatched. However another scientist questioned this explanation on the grounds that it would he very unlikely that conditions would allow generations of turtles over hundreds of millions of years to keep going back to the same nesting ground every single year. So, what is the connection to DNA? Well, there are groups of green turtles that nest in locations other than he Ascension Island. If green turtles always return to the place where they were hatched, then the turtles that have been going to the Ascension Island to nest would have been genetically isolated long enough to have DNA that was very different from the green turtles that nest elsewhere. But when scientists examined DNA from these turtles, their DNA wasn't that different from the DNA of the turtles that go to Ascension Island. Do you have shock? Well, we still don't know the answer to the question about why a certain group of turtles go to Ascension: Island, but this study was a nice example of the usefulness of DNA analysis to biology. How far do some green turtles travel to lay their eggs? 四个选项都是数字，以km或m为单位，由此可以推测本题考查距离。讲座开头就讲道：“每年冬天，一些绿甲海龟都会长途跋涉2000千米，从巴西去阿森松岛……”故选B。