2018年8月26日托福考试难度怎么样?托福阅读部分考了什么?啄木鸟教育老师为大家带来关于本次托福阅读考试的专业分析，希望对大家有帮助!

　　综合点评：

　　作为暑假末的第二场考试，今天的考试依然是采取几套题拼盘的形式，普遍考生觉得较难，特别是加试题目，总体上考试的话题依然是会重复一些这两年考过的文章，以及再现一些TPO文章主题，建议考生们利用好机经和TPO真题来好好复习。

　　Passage one

　　学科分类：生物类

　　题目：Weak Electric Systems in Fish

　　内容回忆：文章开头讲了一种鱼(elephant nose fish)能够通过放电来探测周围水域的物体，这种现象被叫做放电定位(electrolocation)。这种鱼终身都会放电,不过电场很弱,很难被人操作,但是却能形成电场,任何对象进入这个电场都会被扭曲。弱电气系统有一些规则,比如探索新环境即使他们看不到。科学家不仅对electrolocation感兴趣，也对他们对这类鱼的沟通感兴趣,他们发现这些鱼沟通主要的功能有：求偶交配 、侵略行为(aggression )

　　参考阅读：An electric fish is any fish that can generate electric fields. A fish that can generate electric fields is said to be electrogenic while a fish that has the ability to detect electric fields is said to be electroreceptive. Most electrogenic fish are also electroreceptive. Electric fish species can be found both in the ocean and in freshwater rivers of South America (Gymnotiformes) and Africa (Mormyridae). Many fish such as sharks, rays and catfishes can detect electric fields and are thus electroreceptive, but they are not classified as electric fish because they cannot generate electricity. Most common bony fish (teleosts), including most fish kept in aquaria or caught for food, are neither electrogenic nor electroreceptive.

　　Weakly electric fish generate a discharge that is typically less than one volt. These are too weak to stun prey and instead are used for navigation, object detection (electrolocation) and communication with other electric fish (electrocommunication). Two of the best-known and most-studied examples are Peters' elephantnose fish (Gnathonemus petersi) and the black ghost knifefish (Apteronotus albifrons). The males of the nocturnal Brachyhypopomus pinnicaudatus, a toothless knifefish native to the Amazon basin, give off big, long electric hums to attract a mate.

　　The electric organ discharge waveform takes two general forms depending on the species.

　　In some species the waveform is continuous and almost sinusoidal (for example the genera Apteronotus, Eigenmannia and Gymnarchus) and these are said to have a wave-type electric organ discharge. In other species, the electric organ discharge waveform consists of brief pulses separated by longer gaps (for example Gnathonemus, Gymnotus, Leucoraja) and these are said to have a pulse-type electric organ discharge.

　　Passage two

　　学科分类：生物类

　　题目：Dinosaurs and Parental Care

　　内容回忆：(重复2015.2/2018.1.6/2018.7.1真题)文章第一段讲了化石记录无法判断恐龙是否会去照顾后代，一些恐龙巢穴里是有恐龙会在窝里产蛋; 第二段从恐龙巢穴的结构看出恐龙是会进行孵化的，第三段主要讲了亲本抚养依然具有很大争议性; 第四段讲到最强有利的证据来源于恐龙的亲缘动物-鸟类和鳄鱼，因为这些动物都展现了亲本抚养，作为来自同一祖先的恐龙也会有亲本抚养。

　　参考阅读：From fossil evidence alone the question of whether or not dinosaurs cared for their young is very difficult to answer. Because behaviors are not preserved in the fossil record, we can only make inferences from indirect evidence. Parental care can be divided into two types of behavior: prehatching (building nests and incubating eggs—for example, sitting on top of them so as to warm the eggs and encourage hatching) and posthatching (feeding the young and guarding the nests). Most of our evidence comes from alleged dinosaur rookeries (places where nests are built). Several have been excavated in eastern Montana, where a large concentration of dinosaur nests was found at a place now called Egg Mountain. Most of these probably belonged to the hadrosaur Maiasaura. Preserved in these nests are the bones of baby dinosaurs. The finds at Egg Mountain and other sites around the world document that dinosaurs laid their eggs in nests.

　　The nests at Egg Mountain are reported to be equally spaced, separated by a space corresponding to the length of an adult Maiasaura. From this arrangement scientists have inferred that the nests were separated in this way to allow incubation in a tightly packed nesting colony. Although this interpretation is open to challenge, the discovery of Oviraplor adults on top of Oviraplor egg clutches (as determined by embryos in some eggs), is relatively powerful evidence that at least these dinosaurs incubated their nests.

　　Evidence for parental care following hatching is much more controversial. Behavioral speculation based on indirect fossil evidence is dangerous because the data is not always as unambiguous as might appear. At Egg Mountain, many nests contain baby dinosaur bones. Not all the dinosaurs in the nest are the same size. Many of the small bones found in the nests are associated with jaws and teeth, teeth that show signs of wear. It seems reasonable to assume that the wear was caused by the chewing of the coarse plants that were the hatchlings’ diet. Because the young were still in the nest, this food may have been brought to the rookery by foraging adults. This line of reasoning suggests that these animals had an advanced system of parental care. A closer look at the evidence clouds this interpretation. Analysis of dinosaur embryos indicates that worn surfaces are present on the teeth of juveniles even before hatching. Just as a human baby moves inside the mother before birth, modern-day archosaurs also grind their teeth before birth, wearing the surface in some spots. Thus, the fossil evidence for an advanced parental care system in extinct dinosaurs is suggestive but inconclusive, and it is hard even to imagine the sort of paleontologic discovery that could settle this debate for good.

　　The strongest evidence that extinct dinosaurs had some form of advanced parental care system is based on an understanding of the phylogenetic relationships among dinosaurs and their closest living relatives. Living dinosaurs (birds), even primitive ones such as ostriches and kiwis, exhibit parental care, so some form of parental care can be inferred to have existed in the last common ancestor of all birds. Although unappreciated, crocodiles are reptiles that are also caring parents. They build nests, guard the nests, and in some cases dig their young out of the nest when they hear the chirping young ones hatching. The young even communicate with each other while still in the egg by high-frequency squeaks (as birds do). Some evidence suggests that this squeaking is a cue for the synchronization of the hatching. Since birds and crocodiles share a common ancestor, the simplest explanation for the characteristics they share (such as nest building and some form of parental care) is that they evolved only once—that these attributes were present in their common ancestor and passed on to its descendants. Because extinct dinosaurs also descended from that ancestor, the simplest and most general theory is that extinct dinosaurs also shared these characteristics, even though they cannot be directly observed, and we cannot be sure how elaborate their parental care was.

　　Passage three

　　学科分类：自然科学类

　　题目：The Formation of Earth’s Atmosphere

　　内容回忆：(重复2016年11月26日以及2017年3月11日)文章开头提到了地球早期的大气里是只有氢气和氦气，因为地球原始大气非常炎热，构成原始地球大气层的气体分子的一个特点是会不断地高速移动，有一个极端的假设是如果这些分子不是互相抵消中和的话,地球的大气层到最后就会消失;另一个关于这些气体分子的特点是当这些气体分子移动速度快到一定程度时，这些气体是可以不受地心引力的控制的，氢气和氧气是损失的最多的两类气体分子;地球上的火山爆发带来了水蒸气和二氧化碳，水蒸气凝结为现在的海洋;在原始的大气中是没有氧气的，但是有一类细菌是厌氧性细菌并且可以将空气中的二氧化碳转化为氧气，并且这类细菌最后会沉淀构成了现在的海床;最后一段是讲为什么氮气是现在大气中构成最多的气体，氮气的形成十分缓慢，但是相比二氧化碳和水蒸气，氮气非常难以消散和离开地球，因此随着时间的推移氮气渐渐成了空气中最主要的构成成分。

　　参考阅读：In the 4.6 billion years of Earth’s history, the composition of the atmosphere has changed from a hazy, unfamiliar mix to today’s mostly blue skies. As the atmosphere developed, life began and evolved. The evolution of living things changed the atmosphere, and those changes in turn altered life. As far as we know, the relationship is unique to our planet.

　　To deduce what the atmosphere has been like for billions of years, paleontologists, geologists, and paleoclimatologists study rocks, ancient soils, and fossils. With every new find, they improve and refine their understanding of ancient atmospheres.

　　When Earth formed 4.6 billion years ago from a hot mix of gases and solids, it had almost no atmosphere. The surface was molten. As Earth cooled, an atmosphere formed mainly from gases spewed from volcanoes. It included hydrogen sulfide, methane, and ten to 200 times as much carbon dioxide as today’s atmosphere. After about half a billion years, Earth’s surface cooled and solidified enough for water to collect on it.

　　2.7 billion years ago, bluish-green microscopic organisms called cyanobacteria flourished in Earth’s oceans. They made gaseous, or free, oxygen from carbon dioxide, water, and sunlight—the process called photosynthesis. As cyanobacteria created more free oxygen, the amount of oxygen in the atmosphere reached one percent of today’s level, which is 21 percent.

　　Passage Four

　　学科分类：生物类

　　题目：Theories of Megafauna Extinction

　　内容回忆：这篇加试文章主要围绕大型哺乳动物的灭绝的两个成因的讨论展开—人类活动还是气候变化，文章一共分成五段： 第一和第二段认为是人类活动造成了大型哺乳动物的灭绝并解释了原因，第三段进一步支持前两段认为气候改变不是造成大型哺乳动物灭绝的原因，而最后两段转而支持气候变化是导致大型哺乳动物灭绝的原因。

　　参考阅读：TPO 54-2 Overkill of the North American Megafauna

　　Thousands of years ago, in North America's past, all of its megafauna—large mammals such as mammoths and giant bears—disappeared. One proposed explanation for this event is that when the first Americans migrated over from Asia, they hunted the megafauna to extinction.These people, known as the Clovis society after a site where their distinctive spear points were first found, would have been able to use this food source to expand their population and fill the continent rapidly.Yet many scientists argue against this "Pleistocene overkill" hypothesis. Modern humans have certainly been capable of such drastic effects on animals, but could ancient people with little more than stone spears similarly have caused the extinction of numerous species of animals?Thirty-five genera or groups of species (and many individual species) suffered extinction in North America around 11,000 B.C., soon after the appearance and expansion of Paleo-lndians throughout the Americas (27 genera disappeared completely, and another 8 became locally extinct, surviving only outside North America).

　　Although the climate changed at the end of the Pleistocene, warming trends had happened before. A period of massive extinction of large mammals like that seen about 11,000 years ago had not occurred during the previous 400,000 years, despite these changes. The only apparently significant difference in the Americas 11,000 years ago was the presence of human hunters of these large mammals. Was this coincidence or cause-and-effect?

　　We do not know.Ecologist Paul S. Martin has championed the model that associates the extinction of large mammals at the end of the Pleistocene with human predation.With researcher J. E. Mosimann, he has co-authored a work in which a computer model showed that in around 300 years, given the right conditions, a small influx of hunters into eastern Beringia 12,000 years ago could have spread across North America in a wave and wiped out game animals to feed their burgeoning population.

　　The researchers ran the model several ways, always beginning with a population of 100 humans in Edmonton, in Alberta, Canada, at 11,500 years ago.Assuming different initial North American big-game-animal populations (75-150 million animals) and different population growth rates for the human settlers (0.65%-3.5%), and varying kill rates, Mosimann and Martin derived figures of between 279 and 1,157 years from initial contact to big-game extinction.

　　Many scholars continue to support this scenario.For example, geologist Larry Agenbroad has mapped the locations of dated Clovis sites alongside the distribution of dated sites where the remains of wooly mammoths have been found in both archaeological and purely paleontological contexts.These distributions show remarkable synchronicity (occurrence at the same time).

　　There are, however, many problems with this model.Significantly, though a few sites are quite impressive, there really is very little archaeological evidence to support it.Writing in 1982, Martin himself admitted the paucity of evidence;for example, at that point, the remains of only 38 individual mammoths had been found at Clovis sites. In the years since, few additional mammoths have been added to the list;there are still fewer than 20 Clovis sites where the remains of one or more mammoths have been recovered, a minuscule proportion of the millions that necessarily would have had to have been slaughtered within the overkill scenario.

　　Though Martin claims the lack of evidence actually supports his model—the evidence is sparse because the spread of humans and the extinction of animals occurred so quickly—this argument seems weak. And how could we ever disprove it?As archaeologist Donald Grayson points out, in other cases where extinction resulted from the quick spread of human hunters—for example, the extinction of the moa, the large flightless bird of New Zealand—archaeological evidence in the form of remains is abundant. Grayson has also shown that the evidence is not so clear that all or even most of the large herbivores in late Pleistocene America became extinct after the appearance of Clovis. Of the 35 extinct genera, only 8 can be confidently assigned an extinction date of between 12,000 and 10,000 years ago.Many of the older genera, Grayson argues, may have succumbed before 12,000 B.C., at least half a century before the Clovis showed up in the American West.

　　Passage Five

　　学科分类：自然科学-地质类

　　题目：How Soil is Formed

　　内容回忆：(重复2014.7.12真题)文章第一段接受啊土壤形成的一些影响因素：比如母质层，气候，地形等，第二段到第三段围绕各个不同影响因素对于土壤形成的影响分别一一介绍，第二段主要讲了母质层的不同对土壤肥沃程度的影响;第三段讲了气候，比如温度的高低对于土壤的湿度的影响;第四段讲了水参与到了土壤的所有生物化学反应中，第五段讲了地形是土壤变化主要影响因素;第六段：植被，动物，细菌和真菌对于土壤形成的影响; 最后一段讲了岩石的风化以及有机物和土壤的矿化的积累沉淀需要很长的时间。

　　参考阅读：TPO 36-1 soil formation

　　Living organisms play an essential role in soil formation. The numerous plants and animals living in the soil release minerals from the parent material from which soil is formed, supply organic matter, aid in the translocation (movement) and aeration of the soil, and help protect the soil from erosion. The types of organisms growing or living in the soil greatly influence the soil's physical and chemical characteristics. In fact, for mature soils in many parts of the world, the predominant type of natural vegetation is considered the most important direct influence on soil characteristics. For this reason, a soil scientist can tell a great deal about the attributes of the soil in any given area simply from knowing what kind of flora the soil supports. Thus prairies and tundra regions, which have characteristic vegetations, also have characteristic soils.

　　The quantity and total weight of soil flora generally exceed that of soil fauna. By far the most numerous and smallest of the plants living in soil are bacteria. Under favorable conditions, a million or more of these tiny, single-celled plants can inhabit each cubic centimeter of soil. It is the bacteria, more than any other organisms, that enable rock or other parent material to undergo the gradual transformation to soil. Some bacteria produce organic acids that directly attack parent material, breaking it down and releasing plant nutrients. Others decompose organic litter (debris) to form humus (nutrient-rich organic matter). A third group of bacteria inhabits the root systems of plants called legumes. These include many important agricultural crops, such as alfalfa, clover, soybeans, peas, and peanuts. The bacteria that legumes host within their root nodules (small swellings on the root) change nitrogen gas from the atmosphere into nitrogen compounds that plants are able to metabolize, a process, known as nitrogen fixation, that makes the soil more fertile. Other microscopic plants also are important in soil development. For example, in highly acidic soils where few bacteria can survive, fungi frequently become the chief decomposers of organic matter.

　　More complex forms of vegetation play several vital roles with respect to the soil. Tress, grass, and other large plants supply the bulk of the soil's humus. The minerals released as these plants decompose on the surface constitute an important nutrient source for succeeding generations of plants as well as for other soil organisms. In addition, trees can extend their roots deep within the soil and bring up nutrients from far below the surface. These nutrients eventually enrich the surface soil when the tree drops its leaves or when it dies and decomposes. Finally, trees perform the vital function of slowing water runoff and holding the soil in place with their root systems, thus combating erosion. The increased erosion that often accompanies agricultural use of sloping land is principally caused by the removal of its protective cover of natural vegetation.

　　Animals also influence soil composition. The faunal counterparts of bacteria are protozoa. These single-celled organisms are the most numerous representatives of the animal kingdom, and, like bacteria, a million or more can sometimes inhabit each cubic centimeter of soil. Protozoa feed on organic matter and hasten its decomposition. Among other soil-dwelling animals, the earthworm is probably the most important. Under exceptionally favorable conditions, up to a million earthworms (with a total body weight exceeding 450 kilograms) may inhabit an acre of soil. Earthworms ingest large quantities of soil, chemically alter it, and excrete it as organic matter called casts. The casts form a high-quality natural fertilizer. In addition, earthworms mix of soil both vertically and horizontally, improving aeration and drainage.

　　Passage Six

　　学科分类：地质类

　　题目：Glacier Effect

　　内容回忆：

　　第一段：冰川对陆地的作用很大，冰川的重量会使大陆表面下降，这个过程时间很长，然后地球表面又要用很长的时间来恢复原来的高度。

　　第二段：讲冰川的移动，随着冰川越来越大， 收到重力的影响，会慢慢地移动，移动过程中会切割岩石，推倒树木，摧毁一切的植被生物。

　　第三段：在平坦的地方形成的冰山会缓慢移动，朝各个方向发展，在山谷形成的冰川，因为垂直角度大，会形成V型冰川。

　　最后一段：冰川会形成很多地形。

　　参考阅读：TPO 15-3 Glacier Formation

　　Glaciers are slowly moving masses of ice that have accumulated on land in areas where more snowfalls during a year than melts. Snow falls as hexagonal crystals, but once on the ground, snow is soon transformed into a compacted mass of smaller, rounded grains. As the air space around them is lessened by compaction and melting, the grains become denser. With further melting, refreezing, and increased weight from newer snowfall above, the snow reaches a granular recrystallized stage intermediate between flakes and ice known as firn. With additional time, pressure, and refrozen meltwater from above, the small firn granules become larger, interlocked crystals of blue glacial ice. When the ice is thick enough, usually over 30 meters, the weight of the snow and firn will cause the ice crystals toward the bottom to become plastic and to flow outward or downward from the area of snow accumulation.

　　Glaciers are open systems, with snow as the system’s input and meltwater as the system's main output. The glacial system is governed by two basic climatic variables: precipitation and temperature. For a glacier to grow or maintain its mass, there must be sufficient snowfall to match or exceed the annual loss through melting, evaporation, and calving, which occurs when the glacier loses solid chunks as icebergs to the sea or to large lakes. If summer temperatures are high for too long, then all the snowfall from the previous winter will melt. Surplus snowfall is essential for a glacier to develop. A surplus allows snow to accumulate and for the pressure of snow accumulated over the years to transform buried snow into glacial ice with a depth great enough for the ice to flow. Glaciers are sometimes classified by temperature as faster-flowing temperate glaciers or as slower-flowing polar glaciers.

　　Glaciers are part of Earth’s hydrologic cycle and are second only to the oceans in the total amount of water contained. About 2 percent of Earth’s water is currently frozen as ice. Two percent may be a deceiving figure, however, since over 80 percent of the world’s freshwater is locked up as ice in glaciers, with the majority of it in Antarctica. The total amount of ice is even more awesome if we estimate the water released upon the hypothetical melting of the world’s glaciers. Sea level would rise about 60 meters. This would change the geography of the planet considerably. In contrast, should another ice age occur, sea level would drop drastically. During the last ice age, sea level dropped about 120 meters.

　　Passage Seven

　　学科分类：历史类

　　题目：美索不达米亚和埃及

　　内容回忆：主要讲美索不达米亚人和埃及人的主要区别。

　　前三段在讲m的城市，决定市中心的位置和大小主要取决于时候能从别的城市获得食物的能力，因此在市中心人口最多，城市的人口分布不均匀;不同城市之间的间隔是由城墙来区别的;主要的business是手工艺品;后两段讲的是埃及，埃及的城市是均匀分布的，分布在尼罗河附近，大家都有相对均衡的资源来源，不同城市之间不需要有竞争;埃及的主要生意来源是trading and shipping，因为靠着河岸边有很多港口;不同小城市之间不需要由城墙去区分开来，大家生活的都很融洽

　　参考阅读：The ancient civilizations of Mesopotamia and Egypt were both facilitated by rivers that ran in their midst. The Euphrates, Tigris, and the Nile deposited silt along riverbanks which made the adjoining land extremely fertile. This led to the development of cities like Ur and Eriku in Mesopotamia, and Thebes in ancient Egypt. In Egypt, the Nile served as a means of transportation and also provided protection from enemies because its marshy deltas made invasion almost impossible. Ancient Egypt and Mesopotamia, though, had fundamental differences in the way their societies were ruled, as well as in developments concerning cultural and religious life.

　　Ancient Egypt had a different political structure from Mesopotamia. In ancient Egypt, the Pharaoh was considered to be the representative of the gods on earth. The citizens of ancient Egypt believed that their Pharaoh was a god, and refrained from looking directly at his face even when addressed by him (Richards & Van Buren, 2000). The majority of noblemen who were appointed to significant positions in ancient Egypt were related to the Pharaoh. Upon his death, only a son of the Pharaoh could succeed him. In ancient Mesopotamia, society consisted of self-governing regional states for ten centuries before Sargon the Great was proclaimed as king in 2370 BCE (Brisch et al., 2008). The citizens of Mesopotamia, however, did not consider the king or his successors to be divine. In Mesopotamia, most of the scribes were the members of noble families and not related to ruling kings.

　　Another major difference between ancient Egypt and Mesopotamia has to do with religion and culture. In Mesopotamia, women could get permits to participate in trade, and even managed property. However, there were rules enshrined in the Code of Hammurabi which prevented them from inheriting property once their husbands died (Suter & Croddy, 1983). In ancient Egypt, though, women were allowed to take over a third of their husbands’ properties when they became widows. Ancient Egypt and Mesopotamia had highly evolved cultures which supported the development of writing styles and languages.

　　In Mesopotamia, the Sumerians developed the writing system known as cuneiform to facilitate the preservation of records (Richards & Van Buren, 2000). Cuneiform, which was expressed through pie shapes, was written in clay tablets which would then be exposed to the sun to dry. In ancient Egypt, the scribes used hieroglyphics to express ideas and concepts. This language had alphabetic elements as well as logos (Richards & Van Buren, 2000).

　　In ancient Egypt, as in Mesopotamia, multiple gods and goddesses were worshipped. In Mesopotamia, large buildings named ziggurats served as temples where worshippers could make sacrifices and pray (Connan, 1999). In ancient Egypt, temples were ordinary house-like structures where rituals were often conducted by priests to appease numerous gods and goddesses. Ancient Egyptians also took care to prepare themselves for the afterlife during their lives on earth.

　　所考词汇：

　　diverse=varied

　　Compensated=make up for

　　Refuge=protected

　　Critically=dangerously

　　Further=additionally

　　Fluctuations=variations

　　Inhibit=slow down

　　Impeded=restriction

　　Distortions=irregularities

　　Temporarily=briefly

　　Peculiar=unusual

　　Classic=typical

　　Remnant=remains

　　Vigorous=lively

　　Ringed=surrounded

　　Constituent=component

　　Gradual=slow

　　Predominate= are in the majority

　　Diffuse=spread

　　Alleged=supposed

　　Controversial=debatable

　　Inconclusive=not decisive

　　Mounting=increasing

　　Depositing=putting

　　本文解析部分由上海环球教育吴申骏老师原创，转载请注明作者及出处。

　　推荐阅读：2018年8月26日托福真题回忆及分析汇总