Official 47 Passage 3


Coral Reefs


Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

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  • A
    Darwin claimed that, of the three types of coral reefs, only an atoll would be able to survive on a sinking platform.
  • B
    Darwin recognized that coral reefs achieved success by growing upward from a sinking land platform and becoming an atoll.
  • C
    Darwin argued that as a coral reef grew up from a sinking island, it would become a fringing reef, then a barrier reef, and finally, with the disappearance of the island, an atoll.
  • D
    Darwin's theory helped explain the disappearance of a number of islands by showing how coral reef growth caused them to sink below the ocean surface.
正确答案: C

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  • An important environment that is more or less totally restricted to the intertropical zone is the coral reef. Coral reefs are found where the ocean water temperature is not less than 21 °C, where there is a firm substratum, and where the seawater is not rendered too dark by excessive amounts of river-borne sediment. They will not grow in very deep water, so a platform within 30 to 40 meters of the surface is a necessary prerequisite for their development. Their physical structure is dominated by the skeletons of corals, which are carnivorous animals living off zooplankton. However, in addition to corals there are enormous quantities of algae, some calcareous, which help to build the reefs. The size of reefs is variable. Some atolls are very large-Kwajelein in the Marshall Islands of the South Pacific is 120 kilometers long and as much as 24 kilometers across-but most are very much smaller, and rise only a few meters above the water. The 2,000 kilometer complex of reefs known as the Great Barrier Reef, which forms a gigantic natural breakwater off the northeast coast of Australia, is by far the greatest coral structure on Earth.

    Coral reefs have fascinated scientists for almost 200 years, and some of the most pertinent observations of them were made in the 1830s by Charles Darwin on the voyage of the Beagle. He recognized that there were three major kinds: fringing reefs, barrier reefs, and atolls; and he saw that they were related to each other in a logical and gradational sequence. A fringing reef is one that lies close to the shore of some continent or island. Its surface forms an uneven and rather rough platform around the coast, about the level of low water, and its outer edge slopes downwards into the sea. Between the fringing reef and the land there is sometimes a small channel or lagoon. When the lagoon is wide and deep and the reef lies at some distance from the shore and rises from deep water it is called a barrier reef. An atoll is a reef in the form of a ring or horseshoe with a lagoon in the center.

    Darwin's theory was that the succession from one coral reef type to another could be achieved by the upward growth of coral from a sinking platform, and that there would be a progression from a fringing reef, through the barrier reef stage until, with the disappearance through subsidence (sinking) of the central island, only a reef-enclosed lagoon or atoll would survive. A long time after Darwin put forward this theory, some deep boreholes were drilled in the Pacific atolls in the 1950s. The drill holes passed through more than a thousand meters of coral before reaching the rock substratum of the ocean floor, and indicated that the coral had been growing upward for tens of millions of years as Earth's crust subsided at a rate of between 15 and 51 meters per million years. Darwin s theory was therefore proved basically correct. There are some submarine islands called guyots and seamounts, in which subsidence associated with sea-floor spreading has been too speedy for coral growth to keep up.

    Like mangrove swamps, coral reefs are extremely important habitats. Their diversity of coral genera is greatest in the warm waters of the Indian Ocean and the western Pacific. Indeed, they have been called the marine version of the tropical rain forest, rivaling their terrestrial counterparts in both richness of species and biological productivity. They also have significance because they provide coastal protection, opportunities for recreation, and are potential sources of substances like medicinal drugs. At present they are coming under a variety of threats, of which two of the most important are dredging and the effects of increased siltation brought about by accelerated erosion from neighboring land areas.

  • 或多或少完全局限于热带的重要环境是珊瑚礁。珊瑚礁在水温不低于21°C的海洋中被发现,那里有坚实的底层,并且海水中不不因为过量的河流沉积物而显得太暗。它们不会在深海里生长,所以一个有30到40米表面的地台是其发展的必要前提。它们的物理结构主要取决于珊瑚的骨骼,它们是以浮游动物为食的食肉动物。然而,除了珊瑚,还有大量的藻类帮助建立珊瑚礁(一些富含钙质的)。珊瑚礁的大小是多种多样的。一些环礁是非常巨大的一南太平洋的马绍尔群岛的Kwajelein有120公里长,24公里宽一^但大多数都是非常小的,而伸出水面才几米。被称为大堡礁2000千米的珊瑚礁群,是迄今为止最大的珊瑚结构之一,它在澳大利亚东北海岸形成一个巨大的天然堤。



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    高亮句告诉我们达尔文关于珊瑚礁演化的理论:随着珊瑚所生长的平台不断下沉,珊瑚会不断向上生长,这个过程使得珊瑚礁得以向下一个种类演化;演化的顺序是由fringing reefbarrier reef过渡,最终在中心岛沉没消失之后形成atoll




    选项C提到“达尔文认为随着珊瑚所生长的平台不断下沉,珊瑚会不断向上生长,演化的顺序是由fringing reefbarrier reef过渡,最终在中心岛沉没消失之后形成 atoll”与高亮句意思一致,正确