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

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

admin2011-01-17  65
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 exarcebated by the fact that the Martian rocks were ejected
Line    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.
The passage suggests that which of the following is true concerning the probability that a given collision on Mars would eject fragments that will hit the Earth?
选项 A、The probability is higher if the impact produces a crater larger than three kilometers.
B、The probability is lower if the impact produces a crater smaller than three kilometers.
C、The probability is decreased when the impact comes from an area of Mars covered by debris.
D、The probability is decreased when the fragments produced by the impact are larger than 10 centimeters.
E、The probability is decreased when the fragments produced by the impact are younger.
答案C
解析
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