Because of itsaccuracy in outlining the Earth’s subsurface, the seismic-reflection methodremains the most important tool in the search for petroleum reserves. In field practice,a subsurface is mapped by arranging a series of wave-train sources, such assmall dynamite explosions, in a grid pattern. As each source is activated, itgenerates a wave train that moves downward at a speed determined uniquely bythe rock’s elastic characteristics. As rock interfaces are crossed, the elasticcharacteristics encountered generally change abruptly, which causes part of theenergy to be reflected back to the surface, where it is recorded by seismicinstruments. The seismic records must be processed to correct for positionaldifferences between the source and the receiver, for unrelated wave trains, andfor multiple reflections from the rock interfaces. Then the data acquired ateach of the specific source locations are combined to generate a physicalprofile of the subsurface, which can eventually be used to select targets fordrilling.
1.The passage is primarily concerned with
(A) describingan important technique
(B) discussinga new method
(C)investigating a controversial procedure
(D) announcinga significant discovery
(E) promoting anovel application
2. According to the passage, in theseismic-reflection method all of the following have a significant effect on thesignal detected by the seismic instruments EXCEPT the
(A) presence ofunrelated wave trains
(B) placementof the seismic instruments
(C) number ofsources in the grid pattern
(D) nature ofthe reflectivity of the rock interfaces
(E) propertiesof rocks through which the wave train has traveled
3. It can be inferred from the passagethat the seismic-reflection method would be likely to yield an inaccuratephysical profile of the subsurface in which of the following circumstances?
(A) If the speed at which the wave train moved downward changed
(B) If the receiver were not positioned directly at the wave-train source
(C) If the rockon one side of a rock interface had similar elastic characteristics to those ofthe rock on the other side
(D) If the seismic records obtained for the different sources in a grid were highlysimilar to each other
(E) If there were no petroleum deposits beneath the area defined by the grid of wave-trainsources
4. Which of the following best describesthe organization of the passage?
(A) A method iscriticized, and an alternative is suggested.
(B) An illustration is examined, and some errors are exposed.
(C) An assertion is made, and a procedure is outlined.
(D) A series of examples is presented, and a conclusion is drawn.
(E) A hypothesis is advanced, and supporting evidence is supplied.
关于文章：
Because of its accuracy in outlining the Earth’s subsurface, the seismic-reflection method remains the most important tool in the search for petroleum reserves. // In field practice, a subsurface is mapped by arranging a series of wave-train sources, such as small dynamite explosions, in a grid pattern. As each source is activated, it generates a wave train that moves downward at a speed determined uniquely by the rock’s elastic characteristics. As rock interfaces are crossed, the elastic characteristics encountered generally change abruptly, which causes part of the energy to be reflected back to the surface, where it is recorded by seismic instruments. The seismic records must be processed to correct for positional differences between the source and the receiver, for unrelated wave trains, and for multiple reflections from the rock interfaces. Then the data acquired at each of the specific source locations are combined to generate a physical profile of the subsurface, which can eventually be used to select targets for drilling.
主旨，显然是全文首句：Because of its accuracy in outlining the Earth’s subsurface, the seismic-reflection methodremains the most important tool in the search for petroleum reserves. 因为这句话存在明显关键词，because of提示因果关系，某某method提示论述对象，most important 提示重要评价!这些信息永远都是阅读中最重要的。
细节部分一共5个句子，全部在陈述如何获得data。本末句信息可见：Then the data acquired at each of the specific source locations are combined to generate aphysical profile of the subsurface, which can eventually be used to selecttargets for drilling. 这句中then the data acquired几个关键词明显提示了这段话细节在讲什么，是不是很明确?!!
细节部分涉及的考点：第三句 uniquely，特殊关键词;第四句，causes，提示因果关系;第五句，for…for…for…，列举!
到目前为止这篇文章的重点已经跃然纸上了，不是吗?
关于习题：
第一题：A。主旨题当然对应考点主旨句。describe符合说明文特征;important符合主旨句的关键词;technique，method的同义改写!还能是其他选项吗?这一看就是正确答案呀~~天啦，真的这么简单!
第二题：C。这题首先明确与中间那部分细节有关系。其次，看到文中第五句考点列举for… for… for…分别对应选项BAD，这三个选项排除!剩下的CE好说，E对应第三句考点uniquely，排除!所以，选C喽。原来C对应的第二句中a series of，但这不等同于number，也不等同于说number对signal有影响(仔细看题干哦)。
第三题：C。对应第四句考点causes，对change取反有木有?
第四题：C。主旨句remains the most important对应assertion, 下文全部细节就是一个获得data的procedure啦。
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