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Unformatted text preview: om 在在在在在在在在在在在在在在在,在在在在在在在在在在 ○The Yucat region was chosen by geologists as the most probable impact site because of its climate. 4. According to paragraph 3, how did scientists determine that a large meteorite had impacted Earth? ○They discovered a large crater in the Yucat region of Mexico. ○They found a unique layer of sediment worldwide. ○They were alerted by archaeologists who had been excavating in the Yucat region. ○They located a meteorite with a mass of over a trillion tons. Paragraph 4: This impact released an enormous amount of energy, excavating a crater about twice as large as the lunar crater Tycho. The explosion lifted about 100 trillion tons of dust into the atmosphere, as can be determined by measuring the thickness of the sediment layer formed when this dust settled to the surface. Such a quantity of material would have blocked the sunlight completely from reaching the surface, plunging Earth into a period of cold and darkness that lasted at least several months. The explosion is also calculated to have produced vast quantities of nitric acid and melted rock that sprayed out over much of Earth, starting widespread fires that must have consumed most terrestrial forests and grassland. Presumably, those environmental disasters could have been responsible for the mass extinction, including the death of the dinosaurs. 5. The word excavating in the passage is closest in themeaning to ○Digging out ○Extending ○Destroying ○Covering up 6. The word consumed in the passage is closest in the meaning to ○Changed ○Exposed ○Destroyed ○Covered 7. According to paragraph 4, all of the following statements are true of the impact at the end of the Cretaceous period EXCEPT: ○A large amount of dust blocked sunlight from Earth. ○Earth became cold and dark for several months. ○New elements were formed in Earth's crust. ○Large quantities of nitric acid were produced. Paragraph 5: Several other mass extinctions in the geological record have been tentatively identified with large impacts, but none is so dramatic as the Cretaceous event. But even without such specific documentation, it is clear that impacts of this size do occur and that their results can be catastrophic. What is a catastrophe for one group of living things, however, may create opportunities for another group. Following each mass extinction, there is a sudden evolutionary burst as new species develop to fill the ecological niches opened by the event. 8. The phrase tentatively identified in the passage is closest in the meaning to ○Identified after careful study ○Identified without certainty ○Occasionally identified 176 Mail@liuwenyong.com 在在在在在在 www.liuwenyong.com 在在在在在在在在在在在在在在在,在在在在在在在在在在 ○Easily identified Paragraph 6: Impacts by meteorites represent one mechanism that could cause global catastrophes and seriously influence the evolution...
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