托福閱讀真題Official 45 Passage 2（二）

托福閱讀真題Official 45 Passage 2（二）

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 3 of 14

According to paragraph 1,wind-pollinated trees are most likely to be found

A.in temperate forests

B.at lower latitudes

C.in the tropics

D.surrounded by trees of many different species

正確答案：A

題目詳解

題型分類：事實信息題

原文定位：根據(jù)trees定位到第一段第六句

選項分析：

A選項，根據(jù)定位句“如果是在只有相對較少的幾種樹種占主導地位的溫帶森林，花粉的傳播范圍內(nèi)存有眾多相同的樹種，風媒傳播就相對比較安全”。因此推測風媒傳播的樹在溫帶比較多，A選項對應定位句temperate forests。因此選項A正確。

B選項與第二句信息有關(guān)，但第二句說的是higher latitudes。

C選項與第八句信息有關(guān)，但原文說的是animals are a safer bet as transporters of pollen即動物傳播，而不是風傳播。

D選項與最后一句有關(guān)，但這種樹是insect pollinated，而不是風傳播。

Question 4 of 14

Paragraph 1 supports which of the following as the reason animals are a safer bet than wind as pollinators when the individual trees of a species are widely separated?

A.Animals tend to carry pollen from a given flower further than the wind does.

B.Animals serve as pollinators even where there is little wind to disperse the pollen.

C.An animal that visits a flower is likely to deliberately visit other flowers of the same species and pollinate them.

D.Birds and insects fly in all directions,not just the direction the wind is blowing at a given moment.

正確答案：C

題目詳解

題型分類：事實信息題

原文定位：根據(jù)animals are a safer bet定位到第一段倒數(shù)第三句

選項分析：

C選項根據(jù)定位句“相比之下，在熱帶地區(qū)，每一個樹種都有很少的、分布廣泛的個體，風把花粉吹向另一個個體的機會就足夠小了，因此動物作為花粉的轉(zhuǎn)運體是更安全的選擇”。可知樹的數(shù)量較少，而風的傳播方向不固定，所以另一棵樹獲得花粉的幾率就比較小，但動物的情況與風傳播不同。C選項deliberately visit與定位句the chance...is sufficiently slim對應，C選項正確。

A選項的further未提及。

B選項，由倒數(shù)第二句not wind pollinated despite being in windy conditions可知，無論什么時候都不是風媒傳播，B選項因果關(guān)系有誤。

D選項all directions無中生有。

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