托福阅读真题Official 45 Passage 2（四）

托福阅读真题Official 45 Passage 2（四）

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 7 of 14

The word“respectively”in the passage is closest in meaning to

A.over time

B.separately

C.in that order

D.consistently

正确答案：C

题目详解

题型分类：词汇题

选项分析：

词汇所在句“桦树和榛子树的每个花序可分别能产生550万和400万粒花粉，respectively”句子先提到了两种树，后又提到了两个数字。C选项in that order意思为“以那样的顺序”。带入原文符合语境。Respectively原意为“分别地；各自地”。

A选项over time久而久之。

B选项separately意思为not together单独地；分别地。

D选项consistently一贯地，一致地。

因此，选项C符合题干词意。

Question 8 of 14

According to paragraph 3,why do most deciduous wind-pollinated trees produce their pollen in the spring?

A.To avoid competing with evergreen conifers,which flower in the fall or winter

B.So that the leaves of the trees receiving the pollen will not prevent the pollen from reaching the trees’stigmas

C.Because they do not have enough energy to produce new leaves and pollen at the same time

D.In order to take advantage of the windiest time of year

正确答案：B

题目详解

题型分类：事实信息题

原文定位：根据deciduous wind-pollinated trees定位到第三段第三句

选项分析：

B选项，定位句后半部分to reduce the surrounding surfaces that"compete"with the stigmas for pollen中，目的状语to reduce...回答了题干的why提问。B选项the leaves of the trees对应定位句the surrounding surfaces，prevent对应定位句compete。因此B选项正确。

A选项，competing with evergreen conifers与定位句compete矛盾。

C选项，not have enough energy无中生有。

D选项，the windiest time of year无中生有。