托福閱讀真題Official 45 Passage 2（三）

托福閱讀真題Official 45 Passage 2（三）

The Beringia Landscape

During the peak of the last ice age,northeast Asia(Siberia)and Alaska were connected by a broad land mass called the Bering Land Bridge.This land bridge existed because so much of Earth’s water was frozen in the great ice sheets that sea levels were over 100 meters lower than they are today.Between 25,000 and 10,000 years ago,Siberia,the Bering Land Bridge,and Alaska shared many environmental characteristics.These included a common mammalian fauna of large mammals,a common flora composed of broad grasslands as well as wind-swept dunes and tundra,and a common climate with cold,dry winters and somewhat warmer summers.The recognition that many aspects of the modern flora and fauna were present on both sides of the Bering Sea as remnants of the ice-age landscape led to this region being named Beringia.

It is through Beringia that small groups of large mammal hunters,slowly expanding their hunting territories,eventually colonized North and South America.On this archaeologists generally agree,but that is where the agreement stops.One broad area of disagreement in explaining the peopling of the Americas is the domain of paleoecologists,but it is critical to understanding human history:what was Beringia like?

The Beringian landscape was very different from what it is today.Broad,windswept valleys;glaciated mountains;sparse vegetation;and less moisture created a rather forbidding land mass.This land mass supported herds of now-extinct species of mammoth,bison,and horse and somewhat modern versions of caribou,musk ox,elk,and saiga antelope.These grazers supported in turn a number of impressive carnivores,including the giant short-faced bear,the saber-tooth cat,and a large species of lion.

The presence of mammal species that require grassland vegetation has led Arctic biologist Dale Guthrie to argue that while cold and dry,there must have been broad areas of dense vegetation to support herds of mammoth,horse,and bison.Further,nearly all of the ice-age fauna had teeth that indicate an adaptation to grasses and sedges;they could not have been supported by a modern flora of mosses and lichens.Guthrie has also demonstrated that the landscape must have been subject to intense and continuous winds,especially in winter.He makes this argument based on the anatomy of horse and bison,which do not have the ability to search for food through deep snow cover.They need landscapes with strong winds that remove the winter snows,exposing the dry grasses beneath.Guthrie applied the term“mammoth steppe”to characterize this landscape.

In contrast,Paul Colinvaux has offered a counterargument based on the analysis of pollen in lake sediments dating to the last ice age.He found that the amount of pollen recovered in these sediments is so low that the Beringian landscape during the peak of the last glaciation was more likely to have been what he termed a“polar desert,”with little or only sparse vegetation.In no way was it possible that this region could have supported large herds of mammals and thus,human hunters.Guthrie has argued against this view by pointing out that radiocarbon analysis of mammoth,horse,and bison bones from Beringian deposits revealed that the bones date to the period of most intense glaciation.

The argument seemed to be at a standstill until a number of recent studies resulted in a spectacular suite of new finds.The first was the discovery of a 1,000-square-kilometer preserved patch of Beringian vegetation dating to just over 17,000 years ago—the peak of the last ice age.The plants were preserved under a thick ash fall from a volcanic eruption.Investigations of the plants found grasses,sedges,mosses,and many other varieties in a nearly continuous cover,as was predicted by Guthrie.But this vegetation had a thin root mat with no soil formation,demonstrating that there was little long-term stability in plant cover,a finding supporting some of the arguments of Colinvaux.A mixture of continuous but thin vegetation supporting herds of large mammals is one that seems plausible and realistic with the available data.

Question 5 of 14

In paragraph 1,the author compares pollen moved by wind with letters thrown off roofs in order to

A.explain why there are relatively few species of trees that depend on wind pollination

B.compare natural,biological processes with human social practices

C.make a point about the probability of wind-blown pollen reaching a tree of the same species

D.argue against the common assumption that the tallest trees are the most likely to employ wind pollination

正確答案：C

題目詳解

題型分類：修辭目的題

題干分析：考察句子之間的關(guān)系

選項(xiàng)分析：

C選項(xiàng)題干出自第五句。作者此處做了一個(gè)比喻，比喻一般用于解釋前一句觀點(diǎn)。前一句說風(fēng)會(huì)把花粉帶到哪里非常不確定，C選項(xiàng)the probability對(duì)應(yīng)第四句obviously unspecific，reaching a tree of the same species對(duì)應(yīng)第四句where it takes the pollen。因此C選項(xiàng)正確。

A選項(xiàng)relatively few species與第二句it is surprisingly common矛盾。

B選項(xiàng)compare是這句話的內(nèi)容，不是這句話的目的。

D選項(xiàng)tallest trees無中生有。

Question 6 of 14

Paragraph 2 suggests that wind-pollinated plants do not have bright petals,nectar,and scent for which TWO of the following reasons?To receive credit,you must select TWO answers.

A.They interfere with pollination by wind.

B.They are easily damaged by wind.

C.They are unnecessary.

D.They reduce the amount of pollen that can be produced.

正確答案：AC

題目詳解

題型分類：事實(shí)信息題

原文定位：根據(jù)選項(xiàng)定位

選項(xiàng)分析：

A選項(xiàng)interfere對(duì)應(yīng)第二句impediment（妨礙；阻礙；障礙）。

C選項(xiàng)unnecessary對(duì)應(yīng)第一句no need。

B選項(xiàng)damaged無中生有。

D選項(xiàng)reduce the amount無中生有。

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