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A dragonfly barely an inch and a half long appears to be the animal world's most productive long distance traveler — flying thousands of miles over oceans as it migrates from continent to continent — according to a newly published research.
Biologists who led the study say the evidence is in the genes.They found that populations of this dragonfly, called Pantala flavescens, in Texas, eastern Canada，Japan, Korea, India, and South America, have genes so similar that there is only one likely explanation.Apparently — somehow — these insects are travelling distances that are extraordinarily long for their small size, breeding (繁殖) with each other, and creating a common worldwide gene pool.
But how do insects from different continents manage to meet and hook up？Ware says it appears to be the way their bodies have evolved.“These dragonflies have adaptations such as increased surface areas on their wings that enable them to use the wind to carry them.”
Dragonflies, in fact, have already been observed crossing the Indian Ocean from Asia to Africa.“They are following the weather，”says Daniel Troast, who analyzed the DNA samples in Ware's lab.“They're going from India where it's the dry season to Africa where it's the wet season, and apparently they do it once a year.”
Wetness is a must for Pantala to reproduce, and that, says Ware, is why these insects would be driven to even attempt such a dangerous trip, which she calls a “kind of suicide”．The species depends on it.While many will die on the route, as long as enough make it, the species survives.
For the moment, the details of this extraordinary insect travel are a best educated guess.Much more work is needed to bring many loose ends together.Ware and Troast hope that scientists can work on plotting those routes.
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语篇解读：本文是一篇说明文。文章介绍了一种长途飞行的蜻蜓Pantala flavescens。这种蜻蜓冒险长途飞行的原因是它的繁殖需要湿润的气候。
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1．What proves Pantala flavescens are the world's longestdistance flyers?
A．Scientists have tracked the dragonfly across the world.
B．There are many Pantala flavescens in various continents.
C．The same dragonfly was found both in Asia and America.
D．Pantala flavescens in different continents have similar genes.
解析：选D 推理判断题。根据第二段内容可知，领导这项研究的生物学家说基因就是证据。Pantala flavescens蜻蜓在不同的洲有可能留有后代，才会有相似的基因。反过来，在不同的洲有共同的基因，证明了它们曾飞到过那儿，也就证明了这种蜻蜓是长途飞行者。
2．What helps Pantala flavescens fly over so long distance?
A．Their special body shape.
B．Their ability to use wind.
C．Their small and light bodies.
D．Their large and strong wings.
解析：选B 推理判断题。根据第三段中的These dragonflies have adaptations such as increased surface areas on their wings that enable them to use the wind to carry them.可知，这些蜻蜓适应性强，比如翅膀上表面积的增加，使它们能够利用风来飞行。故B项(运用风飞行的能力)正确。
3．What is necessary for Pantala flavescens to reproduce?
A．Damp weather. B．Enough sunshine.
C．Dry environment. D．Warm nests.
解析：选A 细节理解题。根据第五段首句中的Wetness is a must for Pantala to reproduce 可知，这种蜻蜓的繁殖必须要湿润的气候。
4．What does the underlined word “it”in Paragraph 5 refer to?
A．The weather. B．The insect.
C．The wind. D．The trip.
解析：选D 代词指代题。根据第五段内容可知，对于这种昆虫来说，这种危险的长途飞行是自杀式行为。虽然许多昆虫会死在途中，但这种物种依靠这种长途飞行生存下来。从后面一句While many will die on the route, as long as enough make it, the species survives.可知，it指上文的危险长途飞行。
