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单选题

A．Teach their young how to swim.
B．Mate and lay eggs.
C．Hide from predators.
D．Eat different kinds of fish.

参考答案B

解析:I've mentioned how DNA have 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 2000 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 question this explanation on the ground that it would be 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 the 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' ve been genetically isolated long enough to have DNA that was very different from the green turtles that nest else where. But when scientists examine DNA from these turtles, their DNA wasn't that different from the DNA of the turtles that go to Ascension Island. Do you have a 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.
解析
What do green turtles do when they get to Ascension Island?
细节题。根据Every winter some green turtles make a 2000 kin journey from Brazil to Ascension Island in the middle of Atlantic, where they mate and lay eggs.
可知．绿乌龟返回阿森松岛是为了交配和产卵。因此，正确答案是B。

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单选题

A．Its geography is similar to Brazil's.
B．Their instinct leads them to the place they were hatched.
C．There are other species of turtles located there.
D．Its climate is milder than Brazil' s.

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单选题

A．To discover how long their ancestors lived.
B．To analyze how their appearance has evolved.
C．To find out how a disease has spread
D．To determine how closely groups of turtles are related.

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单选题

A．To demonstrate George Washington's survival skills.
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C．To describe a historical event that was portrayed in a painting.
D．To tell a story that George Washington told about himself.

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