400句托福阅读长难句.pdf

精选400句托福阅读长难句(OG&TPO)第一类1.The same thing happens to this day,though on a smaller scale,wherever a sediment-laden river or stream emerges from a mountain valley onto relatively flat land,dropping its load as the current slows:the water usually spreads out fanwise,depositing the sediment in the form of a smooth,fan-shaped slope.2.In lowland country almost any spot on the ground may overlie what was once the bed of a river that has since become buried by soil;if they are now below the waters upper surface(the water table),the gravels and sands of the former riverbed,and its sandbars,will be saturated with groundwater.3.But note that porosity is not the same as permeability,which measures the ease with which water can flow through a material;this depends on the sizes of the individual cavities and the crevices linking them.4.If the pores are large,the water in them will exist as drops too heavy for surface tension to hold,and it will drain away;but if the pores are small enough,the water in them will exist as thin films,too light to overcome the force of surface tension holding them in place;then the water will be firmly held.5.But the myths that have grown up around the rites may continue as part of the groups oral tradition and may even come to be acted out under conditions divorced from these rites.6.Another,advanced in the twentieth century,suggests that humans have a gift for fantasy,through which they seek to reshape reality into more satisfying forms than those encountered in daily life.7.For example,one sign of this condition is the appearance of the comic vision,since comedy requires sufficient detachment to view some deviations from social norms as ridiculous rather than as serious threats to the welfare of the entire group.8.Timberline trees are normally evergreens,suggesting that these have some advantage over deciduous trees(those that lose their leaves)in the extreme environments of the upper timberline.9.This is particularly true for trees in the middle and upper latitudes,which tend to attain greater heights on ridges,whereas in the tropics the trees reach their greater heights in the valleys.10.As the snow is deeper and lasts longer in the valleys,trees tend to attain greater heights on the ridges,even though they are more exposed to high-velocity winds and poor,thin soils there.11.Wind velocity also increases with altitude and may cause serious stress for trees,as is made evident by the deformed shapes at high altitudes.12.Some scientists have proposed that the presence of increasing levels of ultraviolet light with elevation may play a role,while browsing and grazing animals like the ibex may be another contributing factor.13.Probably the most important environmental factor is temperature,for if the growing season is too short and temperatures are too low,tree shoots and buds cannot mature sufficiently to survive the winter months.14.Immediately adjacent to the timberline,the tundra consists of a fairly complete cover of low-lying shrubs,herbs,and grasses,while higher up the number and diversity of species decrease until there is much bare ground with occasional mosses and lichens and some prostrate cushion plants.15.In order for the structure to achieve the size and strength necessary to meet its purpose,architecture employs methods of support that,because they are based on physical laws,have changed little since people first discovered them-even while building materials have changed dramatically.16.Some of the worlds finest stone architecture can be seen in the ruins of the ancient Inca city of Machu Picchu high in the eastern Andes Mountains of Peru.17.It works in compression to divert the weight above it out to the sides,where the weight is borne by the vertical elements on either side of the arch.18.The Ogallala aquifer is a sandstone formation that underlies some 583,000 square kilometers of land extending from northwestern Texas to southern South Dakota.19.Unfortunately,the cost of water obtained through any of these schemes would increase pumping costs at least tenfold,making the cost of irrigated agricultural products from the region uncompetitive on the national and international markets.20.Whatever the final answer to the water crisis may be,it is evident that within the High Plains,irrigation water will never again be the abundant,inexpensive resource it was during the agricultural boom years of the mid-twentieth century.21.To take an extreme example,farmlands dominated by a single crop are so unstable that one year of bad weather or the invasion of a single pest can destroy the entire crop.22.Ecologists are especially interested to know what factors contribute to the resilience of communities because climax communities all over the world are being severely damaged or destroyed by human activities.23.The destruction caused by the volcanic explosion of Mount St.Helens,in the northwestern United States,for example,pales in comparison to the destruction caused by humans.24.Many ecologists now think that the relative long-term stability of climax communities comes not from diversity but from the patchiness“of the environment,an environment that varies from place to place supports more kinds of organisms than an environment that is uniform.25.Similarly,a plant or animal cannot squander all its energy on growing a big body if none would be left over for reproduction,for this is the surest way to extinction.26.At the other extreme are competitors,“almost all of whose resources are invested in building a huge body,with a bare minimum allocated to reproduction.27.A new plant will spring up wherever a seed falls on a suitable soil surface,but because they do not build big bodies,they cannot compete with other plants for space,water,or sunlight.28.These plants are termed opportunists because they rely on their seeds falling into settings where competing plants have been removed by natural processes,such as along an eroding riverbank,on landslips,or where a tree falls and creates a gap in the forest canopy.29.Human landscapes of lawns,fields,or flowerbeds provide settings with bare soil and a lack of competitors that are perfect habitats for colonization by opportunists.30.A massive oak claims its ground for 200 years or more,outcompeting all other would-be canopy trees by casting a dense shade and drawing up any free water in the soil.31.It should be noted,however,that the pure opportunist or pure competitor is rare in nature,as most species fall between the extremes of a continuum,exhibiting a blend of some opportunistic and some competitive characteristics.32.Because some paintings were made directly over others,obliterating them,it is probable that a paintings value ended with the migration it pictured.33.One Lascaux narrative picture,which shows a man with a birdlike head and a wounded animal,would seem to lend credence to this third opinion,but there is still much that remains unexplained.34.Perhaps so much time has passed that there will never be satisfactory answers to the cave images,but their mystique only adds to their importance.35.In 1994 there were nearly 20,000 wind turbines worldwide,most grouped in clusters called wind farms that collectively produced 3,000 megawatts of electricity.36.Most were in Denmark(which got 3 percent of its electricity from wind turbines)and California(where 17,000 machines produced 1 percent of the states electricity,enough to meet the residential needs of a city as large as San Francisco).37.In the long run,electricity from large wind farms in remote areas might be used to make hydrogen gas from water during periods when there is less than peak demand for electricity.38.Large wind farms might also interfere with the flight patterns of migratory birds in certain areas,and they have killed large birds of prey(especially hawks,falcons,and eagles)that prefer to hunt along the same ridge lines that are ideal for wind turbines.39.David Douglas,Scottish botanical explorer of the 1830s,found a disturbing change in the animal life around the fort during the period between his first visit in 1825 and his final contact with the fort in 1832.40.The researchers Peter Ucko and AndreeRosenfeld identified three principal locations of paintings in the caves of western Europe:(1)in obviously inhabited rock shelters and cave entrances;(2)in galleries immediately off the inhabited areas of caves;and(3)in the inner reaches of caves,whose difficulty of access has been interpreted by some as a sign that magical-religious activities were performed there.41.Perhaps,like many contemporary peoples,Upper Paleolithic men and women believed that the drawing of a human image could cause death or injury,and if that were indeed their belief,it might explain why human figures are rarely depicted in cave art.42.For example,wild cattle(bovines)and horses are portrayed more often than we would expect by chance,probably because they were larger and heavier(meatier)than other animals in the environment.43.Consistent with this idea,according to the investigators,is the fact that the art of the cultural period that followed the Upper Paleolithic also seems to reflect how people got their food.44.But in that period,when getting food no longer depended on hunting large game animals(because they were becoming extinct),the art ceased to focus on portrayals of animals.45.When the well reaches a pool,oil usually rises up the well because of its density difference with water beneath it or because of the pressure of expanding gas trapped above it.46.More than one-quarter of the worlds oil and almost one-fifth of the worlds natural gas come from offshore,even though offshore drilling is six to seven times more expensive than drilling on land.47.While there are a dozen or more mass extinctions in the geological record,the Cretaceous mass extinction has always intrigued paleontologists because it marks the end of the age of the dinosaurs.48.The explosion lifted about 100 trillion tons of dust into the atmosphere,as can be determined by measuring the thickness of the sediment layer formed when this dust settled to the surface.49.Such a quantity of material would have blocked the sunlight completely from reaching the surface,plunging Earth into a period of cold and darkness that lasted at least several months.50.The explosion is also calculated to have produced vast quantities of nitric acid and melted rock that sprayed out over much of Earth,starting widespread fires that must have consumed most terrestrial forests and grassland.51.Following each mass extinction,there is a sudden evolutionary burst as new species develop to fill the ecological niches opened by the event.52.Earth is a target in a cosmic shooting gallery,subject to random violent events that were unsuspected a few decades ago.53.Early in the century,a pump had come into use in which expanding steam raised a piston in a cylinder,and atmospheric pressure brought it down again when the steam condensed inside the cylinder to form a vacuum.54.The final step came when steam was introduced into the cylinder to drive the piston backward as well as forward thereby increasing the speed of the engine and cutting its fuel consumption.55.Iron manufacturers which had starved for fuel while depending on charcoal also benefited from ever-increasing supplies of coal;blast furnaces with steam-powered bellows turned out more iron and steel for the new machinery.56.He received rudimentary village schooling but mostly he roamed his uncles farm collecting the fossils that were so abundant in the rocks of the Cotswold hills.57.The companies building the canals to transport coal needed surveyors to help them find the coal deposits worth mining as well as to determine the best courses for the canals.58.In 1831 when Smith was finally recognized by the Geological Society of London as the father of English geology”,it was not only for his maps but also for something even more important.59.Maturation of the frontal lobes of the brain continues throughout early childhood,and this part of the brain may be critical for remembering particular episodes in ways that can be retrieved later.60.Demonstrations of infants and toddlers long-term memory have involved their repeating motor activities that they had seen or done earlier,such as reaching in the dark for objects,putting a bottle in a dollsmouth,or pulling apart two pieces of a toy.61.Through hearing stories with a clear beginning,middle,and ending children may learn to extract the gist of events in ways that they will be able to describe many years later.62.The world looks very different to a person whose head is only two or three feet above the ground than to one whose head is five or six feet above it,Older children and adults often try to retrieve the names of things they saw,but infants would not have encoded the information verbally.63.General knowledge of categories of events such as a birthday party or a visit to the doctors office helps older individuals encode their experiences,but again,infants and toddlers are unlikely to encode many experiences within such knowledge structures.64.Physiological immaturity may be part of why infants and toddlers do not form extremely enduring memories,even when they hear stories that promote such remembering in preschoolers.65.In 1947 Norwegian adventurer Thor Heyerdahl drifted on a balsa-log raft westward with the winds and currents across the Pacific from South America to prove his theory that Pacific islanders were Native Americans(also called American Indians).66.Contrary to the arguments of some that much of the pacific was settled by Polynesians accidentally marooned after being lost and adrift,it seems reasonable that this feat was accomplished by deliberate colonization expeditions that set out fully stocked with food and domesticated plants and animals.67.The undisputed pre-Columbian presence in Oceania of the sweet potato,which is a New World domesticate,has sometimes been used to support HeyerdahlsAmerican Indians in the Pacific theories.68.As Patrick Kirch,an American anthropologist,points out,rather than being brought by rafting South Americans,sweet potatoes might just have easily been brought back by returning Polynesian navigators who could have reached the west coast of South America.69.Conditions that promote fossilization of soft-bodied animals include very rapid covering by sediments that create an environment that discourages decomposition.70.This 700-miIIion-year-old formation gives few clues to the origins of modern animals,however,because paleontologists believe it represents an evolutionary experiment that failed.71.At one time,the animals present in these fossil beds were assigned to various modern animal groups,but most paleontologists now agree that all Tommotian fossils represent unique body forms that arose in the early Cambrian period and disappeared before the end of the period,leaving no descendants in modern animal groups.72.These fossil beds