2. 外语
  3. In this part of the Reading section, you will read 2 passages. You will have 40 minutes to read the passages and answer the ques

In this part of the Reading section, you will read 2 passages. You will have 40 minutes to read the passages and answer the ques

admin2013-04-25  0
问题     In this part of the Reading section, you will read 2 passages. You will have 40 minutes to read the passages and answer the questions.
    Most questions in the Reading section are worth 1 point, but the last question for each passage is worth more than 1 point. The directions for the last question include the point value of the question.
    Some passages will include a word or phrase that is underlined. You can see its definition or an explanation in the Glossary box.
    Within each part in the real test, you can go on to the next question by clicking the Next icon. You may skip questions and go back to them later. If you want to go back to previous questions, click the Back icon. You may click the Review icon at any time and the review screen will show you which questions you have answered and which you have not. From the review screen, you can go directly to any question you have already seen in the Reading section.
Continental Drift
    Continental drift, and the subsequent theory of plate tectonics, forms the modern framework for geological study of the Earth. Continental drift stems from scientific notions as early as the 16th century that the Earth’s continents were once a single land mass, which scientists have termed Pangaea, meaning "all lands" in Greek. In 1912, German meteorologist Alfred Wegener proposed that natural forces such as earthquakes and floods broke Pangaea apart between 225 and 200 million years ago, and it eventually fragmented into the continents as we know them today. Wegener based his theory on four major observations: first, the amazing fit of the African and South American continents; second, the similarities of unusually structured plant and animal fossils discovered along the coastlines of South America and Africa, even though they are separated by the Atlantic Ocean; third, similarities in rocks and ice sheets on these two continents; and fourth, evidence that some ancient climates were diametrically opposite of modern ones.
    Wegener’s theory of continental drift would eventually spark a new way of viewing the Earth. Initially, however, colleagues generally dismissed it as absurd, despite the fact that it seemed to complement available scientific information. Their primary criticism was Wegener’s inability to adequately explain how the large masses of land could drift such great distances.
(A) Wegener speculated that they simply plowed through the ocean floor, but English geophysicist Harold Jeffreys refuted that contention, noting that it is physically impossible for a gargantuan mass of solid rock to do so without breaking up.
(B) It was not until the 1950s--two decades after Wegener’s death--that technological advances enabled scientists to confirm Wegener’s hypotheses. Improved techniques in ocean floor mapping revealed that the bottom of the ocean was not mostly flat and featureless as most scientists had speculated, and that geologic processes on land, such as earthquakes and volcanic eruptions, were linked to dynamics on the ocean floor.
(C) Scientists discovered that hot rock boils up from the Earth’s mantle1 near ridges in the middle of the ocean, spreading over the sea floor and forming new oceanic crust.
(D) As this crust spreads, it moves continents an average of one or two centimeters each year. Scientists also found that as new crust forms at ocean ridges, older crust descends into trenches2 at the rim of the Pacific Ocean Basin, effectively recycling the ocean basins and maintaining the Earth at a steady size. Seismic activity is most prominent in earthquake zones parallel to these trenches at the edge of continents, likely due to the fact that sinking crust melts, causing hot rock to bubble up, leading to eruptions and violent quaking.
    These findings on the ocean floor led to the theory of plate tectonics, which holds that the Earth’s outermost layer consists of more than a dozen large and small plates--massive slabs of solid rock, both above and beneath the water--that are drifting about the surface of the Earth, occasionally colliding, rubbing against each other, clustering and separating, and even disappearing completely under one another. These interactions are constantly shaping the face of the planet, signified by the term "tectonics" from the Greek word meaning "to build." The results of plate-tectonic forces are most evident at plate boundaries--narrow zones between plates. At divergent boundaries, plates pull away from each other, creating new crust. A prominent example can be seen in Iceland, which is splitting as the North American Plate moves westward relativeto the Eurasian Plate. At convergent boundaries, crust is destroyed as one plate dives under another. This tends to form mountain ranges on continental, or surface, plates, such as the South American Andes and the Asian Himalayas. At transform boundaries, plates slide horizontally past each other and crust is neither created nor destroyed. Since the plates lack smooth edges, pressure is generally built up and suddenly released, making these types of boundaries--such as the San Andreas Fault in California--particularly susceptible to earthquakes. At a fourth type of boundary, called plate boundary zones, there are broad areas where boundaries are ill-defined and the effects of plate interaction are not well understood. Because plate boundary zones feature at least two large plates and one small plate caught between them, they have complicated geological structures and earthquake patterns. The theory of plate tectonics has gained widespread scientific acceptance, though there still remains debate over specific aspects. One of these, ironically, is the same question that dogged Wegener: What is the nature of the forces propelling the plates?

According to paragraph 2, what causes the Earth to remain the same size?
选项 A、Constant regeneration of oceanic crust.
B、Earthquakes and volcanic eruptions.
C、The movement of divergent boundaries.
D、Interactions at transform boundaries.
答案A
解析 细节题 答案在第二段的最后部分：随着新的海洋地壳在海脊生成，旧的海洋地壳沉入太平洋海盆边缘的海沟，有效地使海盆再生并使地球体积保持不变(…as new crust forms at ocean ridges, older crust descends into trenches…maintaining the Earth at a steady size.)。B项提到的地震和火山喷发与海底动力有关；C项和D项是在第三段对板块构造论的说明中提到的概念。
转载请注明原文地址:https://kaotiyun.com/show/ZKyO777K
0

托福（TOEFL）

相关试题推荐
随机试题
最新回复(0)