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  3. For many years, Antarctica was thought to be only an archipelago whose islands were tied together above sea level by ice. It was

For many years, Antarctica was thought to be only an archipelago whose islands were tied together above sea level by ice. It was

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问题       For many years, Antarctica was thought to be only an archipelago whose islands were tied together above sea level by ice. It was thought to be made up of two small subcontinents--East Antarctica, the larger, and West Antarctica, containing the Antarctic Peninsula. The two continents were supposed to be separated by a large trough, below sea level, that connected the Ross and Weddell Seas.
      Geophysical studies have now revealed a fairly complete picture of the Antarctic landform below its ice cover. We know now that West Antarctica is connected to the main part of the continent by a chain of mountains well above sea level, though largely buried by ice and snow. The bedrock of much of East Antarctica appears to be above sea level.
     Whether mineral wealth lies hidden by the vast ice sheets is unknown. No more than 2 percent of the continent is actual rock outcrop and much of this small and probably unrepresentative sample has yet to be visited by geologists. Certainly no deposits rich enough to be economically useful have been found.
     Geologists now know that the ice-buried rocks of the Antarctic are similar to rocks of the other continents of the world. Minor amounts of potentially valuable minerals have been reported. The presence of petroleum has been speculated upon by several geologists, but none has yet been found. Low-grade deposits of coal are widespread, especially in the Transantarctic Mountains, but there has been no attempt at exploitation. Even if rich mineral deposits were to be found in Antarctica, the cost of removal from this remote and inhospitable land would be exorbitant.
     Interpretation of continental structure is an important objective of any extensive geologic investigation. Yet except for the earth’ s ocean basins, no area the size of Antarctica is so geologically unknown. With 98 percent of the continent covered by ice, it is extremely difficult to decipher the continent’ s general structure. Geologists determine geologic structure by studying rock outcrops, and many of these are small and widely separated. No outcrops are known in the vast interior of East Antarctica.
     Working out the continental structure of Antarctica is analogous to learning that of the entire United States from studies of a few scattered counties in California and mountain ranges scattered at irregular intervals across the country.  
Low-grade deposits of coal have been found in Antarctica’ s ______ .
选项 A、valleys
B、coastline
C、mountains
D、plains
答案C
解析 见文章第四段最后。
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