托福閱讀真題Official 44 Passage 1（七）

托福閱讀真題Official 44 Passage 1（七）

From Fish to Terrestrial Vertebrates

One of the most significant evolutionary events that occurred on Earth was the transition of water-dwelling fish to terrestrial tetrapods(four-limbed organisms with backbones).Fish probably originated in the oceans,and our first records of them are in marine rocks.However,by the Devonian Period(408 million to 362 million years ago),they had radiated into almost all available aquatic habitats,including freshwater settings.One of the groups whose fossils are especially common in rocks deposited in fresh water is the lobe-finned fish.

The freshwater Devonian lobe-finned fish rhipidistian crossopterygian is of particular interest to biologists studying tetrapod evolution.These fish lived in river channels and lakes on large deltas.The delta rocks in which these fossils are found are commonly red due to oxidized iron minerals,indicating that the deltas formed in a climate that had alternate wet and dry periods.If there were periods of drought,any adaptations allowing the fish to survive the dry conditions would have been advantageous.In these rhipidistians,several such adaptations existed.It is known that they had lungs as well as gills for breathing.Cross sections cut through some of the fossils reveal that the mud filling the interior of the carcass differed in consistency and texture depending on its location inside the fish.These differences suggest a saclike cavity below the front end of the gut that can only be interpreted as a lung.Gills were undoubtedly the main source of oxygen for these fish,but the lungs served as an auxiliary breathing device for gulping air when the water became oxygen depleted,such as during extended periods of drought.So,these fish had already evolved one of the prime requisites for living on land:the ability to use air as a source of oxygen.

A second adaptation of these fish was in the structure of the lobe fins.The fins were thick,fleshy,and quite sturdy,with a median axis of bone down the center.They could have been used as feeble locomotor devices on land,perhaps good enough to allow a fish to flop its way from one pool of water that was almost dry to an adjacent pond that had enough water and oxygen for survival.These fins eventually changed into short,stubby legs.The bones of the fins of a Devonian rhipidistian exactly match in number and position the limb bones of the earliest known tetrapods,the amphibians.It should be emphasized that the evolution of lungs and limbs was in no sense an anticipation of future life on land.These adaptations developed because they helped fish to survive in their existing aquatic environment.

What ecological pressures might have caused fishes to gradually abandon their watery habitat and become increasingly land-dwelling creatures.Changes in climate during the Devonian may have had something to do with this if freshwater areas became progressively more restricted.Another impetus may have been new sources of food.The edges of ponds and streams surely had scattered dead fish and other water-dwelling creatures.In addition,plants had emerged into terrestrial habitats in areas near streams and ponds,and crabs and other arthropods were also members of this earliest terrestrial community.Thus,by the Devonian the land habitat marginal to freshwater was probably a rich source of protein that could be exploited by an animal that could easily climb out of water.Evidence from teeth suggests that these earliest tetrapods did not utilize land plants as food;they were presumably carnivorous and had not developed the ability to feed on plants.

How did the first tetrapods make the transition to a terrestrial habitat.Like early land plants such as rhyniophytes,they made only a partial transition;they were still quite tied to water.However,many problems that faced early land plants were not applicable to the first tetrapods.The ancestors of these animals already had a circulation system,and they were mobile,so that they could move to water to drink.Furthermore,they already had lungs,which rhipidistians presumably used for auxiliary breathing.The principal changes for the earliest tetrapods were in the skeletal system—changes in the bones of the fins,the vertebral column,pelvic girdle,and pectoral girdle.

Question 13 of 14

Look at the four squares[■]that indicate where the following sentence could be added to the passage.These would have been deposited by the receding waters of droughts,during which many aquatic animals must have died.Where would the sentence best fit?Click on a square[■]to add the sentence to the passage.

正確答案：A

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關(guān)系。插入句中的關(guān)鍵詞these，指代前面的某內(nèi)容，且為復(fù)數(shù)；也說(shuō)明插入句子和前面句子有銜接關(guān)系。線索詞drought；died，指出內(nèi)容上的關(guān)聯(lián)，說(shuō)明前面提到了與干旱和死亡有關(guān)的內(nèi)容。插入句譯為：干旱時(shí)期，水量減少，水逐漸退去，水生生物會(huì)死掉。這些可以因干旱時(shí)期退去的水量而積存起來(lái)。

選項(xiàng)分析：

A選項(xiàng)此空前面提到氣候變化導(dǎo)致水域有限，死魚(yú)出現(xiàn)等內(nèi)容，可以判斷插入句中these指的就是這些scattered dead fish and other water-dwelling creatures。氣候變化導(dǎo)致水域有限對(duì)應(yīng)插入句中的drought，dead fish對(duì)應(yīng)插入句中died。因此從邏輯和內(nèi)容上都構(gòu)成銜接。

B選項(xiàng)此空前面提到了植物的出現(xiàn)和其他生物的出現(xiàn)，與死亡的詞不構(gòu)成銜接。

C選項(xiàng)此空前面的句子用thus開(kāi)頭，說(shuō)明做總結(jié)，不再提及干旱時(shí)期的具體描述。

D選項(xiàng)此空前面提到了牙齒出現(xiàn)證明的內(nèi)容，為新的信息和內(nèi)容，與插入句子不構(gòu)成邏輯和內(nèi)容上的關(guān)聯(lián)。

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.

Freshwater lobe-finned fish may be the direct ancestors of terrestrial tetrapods.

Answer Choices:

A.

Rhipidistian crossopterygian had features such as primitive lungs and thick fins that could have helped it survive dry periods.

B.

By the Devonian period,lobe-finned fish preferred freshwater habitats to life in the ocean.

C.

During the Devonian,the number of bones increased in the fins of rhipidistians,improving such animals’ability to swim and move over land.

D.

A drier climate and new sources of food on land may have encouraged the lobe-finned fish’s move to a terrestrial existence.

E.

Shortly after the earliest tetrapods developed lungs,plants and other animals began to flourish on land.

F.

Early tetrapods remained closely connected to water,but several of their body structures were adapted for life on land.

正確答案：ADF

題目詳解

題型分類：文章總結(jié)題

題干分析：選擇概括性的正確選項(xiàng)。

選項(xiàng)分析：

A選項(xiàng)是綜合了第二段和第三段的重要信息，為兩段的概括性總結(jié)。Rhipidistian crossopterygian had features such as primitive lungs and thick fins that could have helped it survive dry periods對(duì)應(yīng)第二段的第四、五、六句If there were periods of drought,any adaptations allowing the fish to survive the dry conditions would have been advantageous...It is known that they had lungs as well as gills for breathing。和第三段的前三句A second adaptation of these fish was in the structure of the lobe fins.The fins were thick,fleshy,and quite sturdy,with a median axis of bone down the center...perhaps good enough to allow a fish to flop its way from one pool of water that was almost dry to an adjacent pond that had enough water and oxygen for survival。

D選項(xiàng)對(duì)應(yīng)第四段的重要信息。A drier climate對(duì)應(yīng)第四段的第二句Changes in climate...if freshwater areas became progressively more restricted，new sources of food對(duì)應(yīng)第四段的第三句Another impetus may have been new sources of food第四段后面就是對(duì)此展開(kāi)的具體例子說(shuō)明。

F選項(xiàng)對(duì)應(yīng)第五段的重要信息。Early tetrapods remained closely connected to water對(duì)應(yīng)第五段的第二句...they were still quite tied to water，but several of their body structures were adapted for life on land對(duì)應(yīng)第五段的最后一句The principal changes for the earliest tetrapods were in the skeletal system—changes in the bones of the fins,the vertebral column,pelvic girdle,and pectoral girdle。

B選項(xiàng)中使用preferred這個(gè)詞在文中沒(méi)有表達(dá)過(guò)與此相關(guān)的意思。無(wú)中生有。

C選項(xiàng)說(shuō)到鰭的骨骼數(shù)量增加，提升了游泳和陸上移動(dòng)能力，而文中最后一句The principal changes for the earliest tetrapods were in the skeletal system—changes in the bones of the fins,the vertebral column,pelvic girdle,and pectoral girdle并沒(méi)有說(shuō)骨骼數(shù)量的增加。無(wú)中生有。

E選項(xiàng)說(shuō)在四足動(dòng)物出現(xiàn)肺不久，植物和其他動(dòng)物在陸地上發(fā)展起來(lái)。而原文中developed lungs的內(nèi)容出現(xiàn)在第二段，用來(lái)說(shuō)明魚(yú)進(jìn)化的一個(gè)適應(yīng)性改變。plants and other animals began to flourish on land出現(xiàn)在第四段，用來(lái)說(shuō)明魚(yú)進(jìn)化成陸生生物的原因。兩者之間在文中并無(wú)關(guān)聯(lián)，也不存在先后順序。

譯文

>> 雅思 托福 免費(fèi)測(cè)試、量身規(guī)劃、讓英語(yǔ)學(xué)習(xí)不再困難<<