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  3. Scientists have long sought the reasons for the relatively young age of the majority of Martian meteorites discovered on Ea

Scientists have long sought the reasons for the relatively young age of the majority of Martian meteorites discovered on Ea

admin2009-05-19  49
问题          Scientists have long sought the reasons for the relatively young age of the
     majority of Martian meteorites discovered on Earth in comparison with the age
     of Mars, an enigma exacerbated by the fact that the Martian rocks were ejected
     by only six or seven separate impact events. Previous tests had predicted that
(5)   driving meteorites to Earth would require a collision with an asteroid immense
     enough to make a crater 12-kilometers across, but because such huge impacts
     are extremely infrequent, it was unlikely that enough of them could have
     occurred to explain our planet’s Martian meteorite collection.
         Now astronomer James Head’s higher-resolution models demonstrate that
(10)  collisions making craters only three kilometers across can jettison 10 million
     fragments, each about 10 centimeters across,  into space,  a distribution
     sufficient to cause some of them to be found on Earth. Sections of the planet
     covered by debris (thus likely to be made up of older terrain) would require
     larger and hence rarer impacts, and thus meteorites which reach Earth are
(15)  predictably biased toward younger ages.
选项 A、presenting an argument to support a particular hypothesis
B、suggesting an answer to a theoretical question
C、questioning the assumptions of a research project
D、criticizing experimental results
E、explaining the origin of certain scientific data
答案B
解析
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