托福阅读真题Official 45 Passage 2（二）

托福阅读真题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

正确答案：A

题目详解

题型分类：事实信息题

原文定位：根据trees定位到第一段第六句

选项分析：

A选项，根据定位句“如果是在只有相对较少的几种树种占主导地位的温带森林，花粉的传播范围内存有众多相同的树种，风媒传播就相对比较安全”。因此推测风媒传播的树在温带比较多，A选项对应定位句temperate forests。因此选项A正确。

B选项与第二句信息有关，但第二句说的是higher latitudes。

C选项与第八句信息有关，但原文说的是animals are a safer bet as transporters of pollen即动物传播，而不是风传播。

D选项与最后一句有关，但这种树是insect pollinated，而不是风传播。

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.

正确答案：C

题目详解

题型分类：事实信息题

原文定位：根据animals are a safer bet定位到第一段倒数第三句

选项分析：

C选项根据定位句“相比之下，在热带地区，每一个树种都有很少的、分布广泛的个体，风把花粉吹向另一个个体的机会就足够小了，因此动物作为花粉的转运体是更安全的选择”。可知树的数量较少，而风的传播方向不固定，所以另一棵树获得花粉的几率就比较小，但动物的情况与风传播不同。C选项deliberately visit与定位句the chance...is sufficiently slim对应，C选项正确。

A选项的further未提及。

B选项，由倒数第二句not wind pollinated despite being in windy conditions可知，无论什么时候都不是风媒传播，B选项因果关系有误。

D选项all directions无中生有。