托福閱讀真題Official 45 Passage 2（七）

托福閱讀真題Official 45 Passage 2（七）

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 13 of 14

Look at the four squares[■]that indicate where the following sentence could be added to the passage.This level of volume is important to ensure that at least some of the pollen reaches a target tree,but dispersing the pollen is crucial as well.Where would the sentence best fit?Click on a square[■]to add the sentence to the passage.

正確答案：B

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。插入句開頭說This level of volume，表明前文提到了具體的量，插入句后半部分說到了dispersing the pollen，說明這是下一句的主題。插入句是一個(gè)過渡句。

選項(xiàng)分析：

B選項(xiàng)前一句說5.5 and 4 million grains對應(yīng)插入句This level of volume，B選項(xiàng)后一句the pollen go as far as possible對應(yīng)插入句dispersing the pollen。因此應(yīng)該填入第二個(gè)空。

A選項(xiàng)前一句的a lot of pollen對應(yīng)后一句的5.5 and 4 million grains，兩句之間不需要過渡句。

C選項(xiàng)后面兩句對應(yīng)C選項(xiàng)前面一句的various adaptations，不需要過渡句。

D選項(xiàng)前后都在說dispersing the pollen，不需要過渡句。

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.

Some plants depend on the wind to carry their pollen.

Answer Choices:

A.

Because there are few trees in temperate forests,it is safer to transport pollen by insects or birds.

B.

Most wind-pollinated trees are deciduous because evergreen needles compete with the stigma for pollen,making wind pollination uncertain.

C.

Wind pollination is a safe reproductive strategy for trees in temperate forests where there are only a few dominant species and,therefore,many individuals of the same species.

D.

Wind-pollinated plants usually have small petalless flowers which often grow in catkins that produce a very fine-grained pollen.

E.

Wind pollination requires production of a large amount of pollen,which must be released at the right time and under the right conditions to extend its range.

F.

Wind-pollinated trees must grow in regions that are only moderately windy because strong winds will blow the tiny pollen grains past the stigma.

正確答案：CDE

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：

C選項(xiàng)為第一段重要信息，Wind pollination is a safe reproductive strategy for trees in temperate forests對應(yīng)第一段第二句it is surprisingly common,especially in higher latitudes。there are only a few dominant species and,therefore,many individuals of the same species對應(yīng)第一段第六句。

D選項(xiàng)為第五段重要信息，very fine-grained pollen對應(yīng)第五段第二句smaller。

E選項(xiàng)為第三段和第四段重要信息，a large amount of pollen出自第三段第一句require a lot of pollen，be released at the right time對應(yīng)第四段第四句when the air is dry。under the right conditions對應(yīng)第四段第一句produced higher in the top branches和第二句until the wind is strong enough to bend them。

A選項(xiàng)與第一段信息有關(guān)，但是safer無中生有。

B選項(xiàng)信息與第三段有關(guān)，但是Most wind-pollinated trees are deciduous無中生有。

F選項(xiàng)信息與第五段有關(guān)，但是moderately windy無中生有。并且blow the tiny pollen grains past the stigma與第五段最后一句矛盾。

>> 雅思 托福 免費(fèi)測試、量身規(guī)劃、讓英語學(xué)習(xí)不再困難<<