托福阅读真题Official 47 Passage 3（四）

托福阅读真题Official 47 Passage 3（四）

Coral Reefs

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—Kwajalein 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.

Question 7 of 14

According to paragraph 2,which of the following is NOT characteristic of a barrier reef?

A.It is located away from the shore of the neighboring land.

B.It is separated from neighboring land by a wide channel.

C.It is located in deep ocean water.

D.It surrounds a small,central lagoon.

正确答案：D

题目详解

题型分类：否定事实信息题

原文定位：根据barrier reef定位，整个段落都在讨论这个内容

选项分析：

D选项，定位到原文最后一句An atoll is a reef...with a lagoon in the center，说的是atoll在泻湖中间，而不是堡礁barrier reef的特点，所以选D。

A选项出自倒数第二句紧邻fringing reef，而第二句提到fringing reef挨着shore of some continent or island，说明barrier reef离海岸线不远。

B选项出自倒数第三句barrier reef紧邻宽阔的通道。

C选项出自倒数第二句rises from deep water it is called a barrier reef。

Question 8 of 14

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.

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

题目详解

题型分类：简化句子题

原文分析：原文中有and逻辑词表示并列，提炼的核心内容是Darwin's theory was that...and that...主干中有2个表语从句，再提炼汉语意思：达尔文认为为珊瑚礁从下沉的岛屿上长出来，然后变成裙礁，再变成堡礁，最后岛屿消失变成环礁。

选项分析：

选项C中有then,and finally等逻辑过渡词，意思是：当一个珊瑚礁从一个下沉的岛屿上成长起来的时候，它会变成一个边缘的珊瑚礁，然后变成一个屏障的珊瑚礁，最后随着这个岛的消失，变成一个环礁，也符合原文，选项C正确。

A选项说only an atoll would be able to survive on a sinking platform，“只有环礁能够在下沉的平台上生存”，无中生有。

B选项，achieved success意思是取得成功，原文的“succession”意思是“一连串、继承、衔接”，形近词意思不同，文中并没有讨论珊瑚礁怎么取得成功。

D选项，原文强调的是a reef-enclosed lagoon or atoll would survive，而不是选项中解释disappearance of a number of islands，张冠李戴。