GRE考试

【单选题】Scientists have long sought the reasons for the relatively young age of the majority of Martian meteorites discovered onEarth 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 driving meteorites toEarth 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 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 onEarth. 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 reachEarth are predictably biased toward younger ages.Scientists have long sought the reasons for the relatively young age of the majority of Martian meteorites discovered onEarth 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 driving meteorites toEarth 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 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 onEarth. 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 reachEarth are 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 theEarth
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.

网考网参考答案：C
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