托福閱讀真題Official 47 Passage 3（四）

托福閱讀真題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.

正確答案：D

題目詳解

題型分類：否定事實(shí)信息題

原文定位：根據(jù)barrier reef定位，整個(gè)段落都在討論這個(gè)內(nèi)容

選項(xiàng)分析：

D選項(xiàng)，定位到原文最后一句An atoll is a reef...with a lagoon in the center，說(shuō)的是atoll在瀉湖中間，而不是堡礁barrier reef的特點(diǎn)，所以選D。

A選項(xiàng)出自倒數(shù)第二句緊鄰fringing reef，而第二句提到fringing reef挨著shore of some continent or island，說(shuō)明barrier reef離海岸線不遠(yuǎn)。

B選項(xiàng)出自倒數(shù)第三句barrier reef緊鄰寬闊的通道。

C選項(xiàng)出自倒數(shù)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.

正確答案：C

題目詳解

題型分類：簡(jiǎn)化句子題

原文分析：原文中有and邏輯詞表示并列，提煉的核心內(nèi)容是Darwin's theory was that...and that...主干中有2個(gè)表語(yǔ)從句，再提煉漢語(yǔ)意思：達(dá)爾文認(rèn)為為珊瑚礁從下沉的島嶼上長(zhǎng)出來(lái)，然后變成裙礁，再變成堡礁，最后島嶼消失變成環(huán)礁。

選項(xiàng)分析：

選項(xiàng)C中有then,and finally等邏輯過(guò)渡詞，意思是：當(dāng)一個(gè)珊瑚礁從一個(gè)下沉的島嶼上成長(zhǎng)起來(lái)的時(shí)候，它會(huì)變成一個(gè)邊緣的珊瑚礁，然后變成一個(gè)屏障的珊瑚礁，最后隨著這個(gè)島的消失，變成一個(gè)環(huán)礁，也符合原文，選項(xiàng)C正確。

A選項(xiàng)說(shuō)only an atoll would be able to survive on a sinking platform，“只有環(huán)礁能夠在下沉的平臺(tái)上生存”，無(wú)中生有。

B選項(xiàng)，achieved success意思是取得成功，原文的“succession”意思是“一連串、繼承、銜接”，形近詞意思不同，文中并沒(méi)有討論珊瑚礁怎么取得成功。

D選項(xiàng)，原文強(qiáng)調(diào)的是a reef-enclosed lagoon or atoll would survive，而不是選項(xiàng)中解釋disappearance of a number of islands，張冠李戴。

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