2013年托福考试阅读模拟试题及答案1_第3页

　　Paragraph 5

　　As on the Moon, the extent of large impact cratering (i.e.craters too big to have been filled in by erosion since they were formed) serves as an age indicator for the Martian surface. Age estimates ranging from four billion years for Mars's southern highlands to a few hundred million years in the youngest volcanic areas were obtained in this way.

　　11、According to paragraph 5, what have scientists been able to determine from studies of large impact cratering on Mars?

　　Some Martian volcanoes are much older ithan was once thought.

　　The age of Mars's surface can vary from area to area.

　　Large impact craters are not reliable indicators of age in areas with high volcanic activity.

　　Some areas of the Martian surface appear to be $Wer than they actually are.

　　Paragraph 6

　　The detailed appearance of Martian impact craters provides an important piece of information about conditions just below the planet's surface. Martian craters are surrounded by ejecta (debris formed as a result of an impact) that looks quite different from its lunar counterparts. A comparison of the Copernicus crater on the Moon with the (fairly typical) crater Yuty on Mars demonstrates the differences. The ejecta surrounding the lunar crater is just what one would expect from an explosion ejecting a large volume of dust, soil, and boulders.However, the ejecta on Mars gives the distinct impression of a liquid that has splashed or flowed out of crater. Geologists think that this fluidized ejecta crater indicates that a layer of permafrost, or water ice, lies just a few meters under the surface. Explosive impacts heated and liquefied the ice, resulting in the fluid appearance of the ejecta.

　　12、 According to paragraph 6, the ejecta of Mars's crater Yuty differs from the ejecta of the Moon's Copernicus crater in that the ejecta of the Yuty crater

　　Has now become part of a permafrost layer

　　Contains a large volume of dust, soil and boulders

　　Suggests that liquid once came out of the surface at the crater site

　　Was thrown a comparatively long distance from the center of the crater

　　13、Look at the four squares [■] that indicate where the following sentence could be added to the

　　passage.

　　This surface feature has led to speculation about what may lie under Mars's surface.

　　Where would the sentence best fit? Click on a square to add the sentence to the passage.

　　Paragraph 6

　　The detailed appearance of Martian impact craters provides an important piece of information about conditions just below the planet's surface. Martian craters are surrounded by ejecta (debris formed as a result of an impact) that looks quite different from its lunar counterparts. A comparison of the Copernicus crater on the Moon with the (fairly typical) crater Yuty on Mars demonstrates the differences. The ejecta surrounding the lunar crater is just what one would expect from an explosion ejecting a large volume of dust, soil, and boulders. ■ However, the ejecta on Mars gives the distinct impression of a liquid that has splashed or flowed out of crater. ■ Geologists think that this fluidized ejecta crater indicates that a layer of permafrost, or water ice, lies just a few meters under the surface. ■ Explosive impacts heated and liquefied the ice, resulting in the fluid appearance of the ejecta. ■

　　14、 Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

　　Volcanoes and impact craters are major features of Martian geology.

　　A. Plate motion on Mars, once considered to have played no role in shaping the planets surface, is

　　now seen as being directly associated with the planet's earliest volcanoes.

　　B.Mars has shield volcanoes, some of which are extremely tall because of the planet"s low surface

　　gravity.

　　C. Although the erosive power of the Martian atmosphere ensures that Mars has fewer craters than the

　　Moon does, impact craters are prominent on Mars' s surface.

　　D. Scientists cannot yet reliably estimate the age of the Martian surface because mere has been too

　　much erosion of it.

　　E. Scientists have been surprised to discover that conditions just below the surface of Mars are very

　　similar to conditions just below the surface of the Moon

　　F. Studies of crater ejecta have revealed the possibility of a layer of permafrost below the surface of   Mars.