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OFFICIAL47 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 sentences 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. Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it. Coral reefs constitute an important tropical environment that provides habitat for a rich variety of ocean life.

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Coral Reefs
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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.

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 sentences 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. Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it. Coral reefs constitute an important tropical environment that provides habitat for a rich variety of ocean life.

A.Coral reefs are structures made by living creatures and can grow only in specific ocean conditions.

B.Although atolls can sometimes grow to large proportions, barrier reefs are by far the largest coral structures.

C.Mangrove swamps are as important as coral reefs as the habitat for numerous plant and animal species.

D.Coral reefs are classified as fringing, barrier, or atoll, all of which are linked in a chain of progressive development.

E.Although coral reefs are important to humans in several ways, they are currently threatened by dredging and mud from erosion.

F.Fringing reefs lie close to the shore of continents and islands, forming a transition zone between the land mass and the sea.

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【题目翻译】说明:下面是文章的简要概括的介绍句。通过选择三个答案来完成总结,这三个答案表达了文章中最重要的观点。有些句子不属于摘要,因为它们表达了文章中没有呈现的想法,或者是文章中的次要思想。 瑚礁构成了重要的热带环境,为丰富多样的海洋生物提供了栖息地。 A:珊瑚礁是由生物构成的结构,只有在特定的海洋条件下才能生长。 B:虽然环礁有时会长得很大,但是屏障礁是迄今为止最大的珊瑚结构。 C:红树林沼泽和珊瑚礁一样重要,也是许多动植物的栖息地。 珊瑚礁分为边缘珊瑚礁、屏障珊瑚礁和环礁珊瑚礁,所有这些珊瑚礁都以渐进式发展的链条相连。 E:虽然珊瑚礁在几个方面对人类很重要,但它们目前受到疏浚和泥浆侵蚀的威胁。 F:边缘礁靠近大陆和岛屿的海岸,在陆地和海洋之间形成一个过渡带。 【判定题型】:根据问题的提问方式和6选3的作答方式可以确定该题目为概要小结题。 【选项定位及分析】 A:原文第一段首先介绍珊瑚礁的组成以及生存环境要求,对应选项A中:Coral reefs … living creatures … specific ocean conditions B:B选项错误,原文认为珊瑚礁会不断生长,atoll是最终阶段,因此barrier reef不可能最大. C:选项错误,因为珊瑚礁和热带雨林之间具有生物多样性方面的共同点,而不是珊瑚礁和沼泽之间,选项和原文不符; D:第二段介绍珊瑚礁分类以及它们的进化顺序,对应选项D中:Coral reefs are classified as fringing, barrier, or atoll, … a chain of progressive development. E:第四段介绍珊瑚礁的好处以及它们受到的威胁,对应选项E中:Although coral reefs are important …, … threatened by dredging and mud from erosion。 F:F选项错误, 文章中只说fringing reef和陆地之间会有channel或lagoon,故F选项在原文中未提及。

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