托福閱讀真題Official 47 Passage 3（七）

托福閱讀真題Official 47 Passage 3（七）

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 13 of 14

Look at the four squares[■]that indicate where the following sentence could be added to the passage.Yet because many coral reef organisms can tolerate only a narrow range of environmental conditions,reefs are sensitive to damage from environmental changes.Where would the sentence best fit?Click on a square[■]to add the sentence to the passage.

正確答案：C

題目詳解

題型分類：插入句子題

題干分析：考察句子和句子之間的銜接判斷

選項分析：

待插入句子中邏輯詞yet后面說珊瑚只能容忍極少的環(huán)境條件，推測表示前文講到都是珊瑚礁好的一些方面，后面講傷害。與選項C呼應，前文講珊瑚所帶來的各種好處貢獻，后面講他們也承受這很多威脅。

A選項邏輯錯誤Indeed前后都在講珊瑚好處，中間不能插句子。

B選項邏輯錯誤，選項前后用邏輯詞also銜接很恰當，不必插入句子。

D選項邏輯錯誤，前面講的是珊瑚受到威脅，而與待插入句子前后推測內容不符，錯誤。

Question 14 of 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.

Coral reefs constitute an important tropical environment that provides habitat for a rich variety of ocean life.

Answer Choices:

A.

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

B.

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

C.

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

D.

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

E.

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

F.

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

正確答案：ABD

題目詳解

題型分類：文章總結題

題干分析：選擇概括性的正確選項

選項分析：

正確選項：

A選項為第一段重要信息，第一句中restricted to the intertropical zone對應選項中grow only in specific ocean conditions；第四句中zooplankton對應選項中l(wèi)iving creatures。

B選項為第二段重要信息，第三句three major kinds:fringing reefs,barrier reefs,and atolls對應選項中classified as fringing,barrier,or atoll；logical and gradational sequence對應選項中a chain of progressive development。

D選項對應第四段的重要信息，本段總結了珊瑚的好處和受到的威脅，與選項呼應。

錯誤選項：

C選項出自第三段第一句，但原文認為珊瑚會不斷生長，最后只有atoll can survive，而不是說barrier reefs會稱為最大的，與原文矛盾。

E選項出自第四段第二句，文章說的是珊瑚礁和熱帶雨林之間具有生物多樣性方面的共同點，而不是珊瑚礁和沼澤之間，與原文矛盾。

F選項出自第二段第三句和倒數(shù)第二句，第三句說fringing reef靠近大陸或者島嶼，對應選項前半句，倒數(shù)第三句說fringing reef和陸地之間會有channel或lagoon，而沒提到在大陸和海洋中間形成過渡區(qū)，無中生有。

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