托福-练习十八及答案解析.doc

1、托福-练习十八及答案解析(总分：35.00，做题时间：90 分钟)一、Passage 1(总题数：2，分数：10.00)EFFECTS OF IONIZING RADIATION1 Everyone on Earth is continually exposed to small, relatively harmless amounts of ionizing radiation, known as background radiation, from natural sources such as soil and rock. However, other types of ionizing

2、 radiation-x-rays, ultraviolet radiation from the sun, and alpha, beta, and gamma radiation emitted by radioactive isotopes-have the potential to harm the human body. Ionizing radiation has enough energy to remove one or more electrons from the atoms it hits to form positively charged ions that can

3、react with and damage living tissue. Most damage occurs in tissues with rapidly dividing cells, such as the bone marrow, where blood cells are made, and the digestive tract, whose lining must be constantly renewed.2 Exposure to ionizing radiation can damage cells in two ways. The first is genetic da

4、mage, which alters genes and chromosomes. This can show up as a genetic defect in children or in later generations. The second type of damage is somatic, which causes victims direct harm in the form of bums, miscarriages, eye cataracts, some types of leukemia, or cancers of the bone, thyroid, breast

5、, skin, and lung. Small doses of ionizing radiation over a long period of time cause less damage than the same total dosage given all at once. Exposure to a large dose of ionizing radiation over a short time can be fatal within a few minutes to a few months later.（分数：4.00）(1).According to the passag

6、e, what is one difference between background radiation and other types of ionizing radiation?（分数：1.00）A.Background radiation is rare in nature, while other types are not.B.Background radiation is less likely to harm the human body.C.Background radiation cannot form positively charged ions.D.Backgrou

7、nd radiation causes more damage to the environment.(2).What types of tissues are harmed most by ionizing radiation?（分数：1.00）A.Tissues with cells that divide quicklyB.Tissues on the outside surface of the bodyC.Tissues exposed to background radiationD.Tissues with a large number of chromosomes(3).All

8、 of the following are examples of somatic damage EXCEPT（分数：1.00）A.genetic defectsB.eye cataractsC.radiation burnsD.lung cancer(4).Which exposure to ionizing radiation causes the most serious damage to humans?（分数：1.00）A.Continuous exposure to background radiation in the environmentB.Small doses of io

9、nizing radiation over a long period of timeC.A single dose of a moderate amount of ionizing radiationD.Exposure to a large amount of ionizing radiation in a short periodTHE COYOTE1 All North American canids have a doglike appearance characterized by a graceful body, long muzzle, erect ears, slender

10、legs, and bushy tail. Most are social animals that travel and hunt in groups or pairs. After years of persecution by humans, the populations of most North American canids, especially wolves and foxes, have decreased greatly. The coyote, however, has thrived alongside humans, increasing in both numbe

11、rs and range.2 Its common name comes from coyotl, the term used by Mexicos Nahuatl Indians, and its scientific name, canis latrans, means “barking dog.“ The coyotes vocalizations are varied, but the most distinctive are given at dusk, dawn, or during the night and consist of a series of barks follow

12、ed by a prolonged howl and ending with short, sharp yaps. This call keeps the band alert to the locations of its members. One voice usually prompts others to join in, resulting in the familiar chorus heard at night throughout the West.3 The best runner among the canids, the coyote is able to leap fo

13、urteen feet and cruise normally at 25-30 miles per hour. It is a strong swimmer and does not hesitate to enter water after prey. In feeding, the coyote is an opportunist, eating rabbits, mice, ground squirrels, birds, snakes, insects, many kinds of fruit, and carrion-whatever is available. To catch

14、larger prey, such as deer or antelope, the coyote may team up with one or two others, running in relays to tire prey or waiting in ambush while others chase prey toward it. Often a badger serves as involuntary supplier of smaller prey: while it digs for rodents at one end of their burrow, the coyote

15、 waits for any that may emerge from an escape hole at the other end.4 Predators of the coyote once included the grizzly and black bears, the mountain lion, and the wolf, but their declining populations make them no longer a threat. Man is the major enemy, especially since coyote pelts have become in

16、creasingly valuable, yet the coyote population continues to grow, despite efforts at trapping, shooting, and poisoning the animals.（分数：6.00）(1).According to the passage, the coyote is unlike other North American canids in what way?（分数：1.00）A.The coyotes body is not graceful.B.The coyote is not hunte

17、d by humans.C.The coyote population has not decreased.D.The coyote does not know how to swim.(2).All of the following statements describe the coyotes vocalizations EXCEPT:（分数：1.00）A.Vocalizations communicate the locations of other coyotes.B.The coyote uses its distinctive call to trick and catch pre

18、y.C.A group of coyotes will often bark and howl together.D.The coyotes scientific name reflects its manner of vocalizin(3).According to the passage, the coyote is an opportunist because it（分数：1.00）A.nows how to avoid being capturedB.likes to team up with other coyotesC.has better luck than other pre

19、datorsD.takes advantage of circumstances(4).Which animal sometimes unknowingly helps the coyote catch food?（分数：1.00）A.WolfB.RodentC.DeerD.Badger(5).According to the passage, the chief predator of the coyote is（分数：1.00）A.the wolfB.the mountain lionC.the humanD.the grizzly bear(6).According to the pas

20、sage, all of the following statements are true EXCEPT:（分数：1.00）A.The coyote is a serious threat to human activities.B.The coyote is a skillful and athletic predator.C.The coyote hunts cooperatively with other coyotes.D.The coyote survives despite persecution by humans.二、Passage 2(总题数：3，分数：25.00)RURA

21、L CANADA1 In the 1880s, over three-fourths of Canadas population lived outside urban centers. One view of rural Canada at that time portrays it as a vast wasteland of isolated farm communities. However, a more accurate view shows that rural Canadians had access to considerable information. The posta

22、l service was efficient and inexpensive and connected rural Canadians with the outside world. Many farm families received at least one newspaper through the mail, usually within a day of publication. The daily newspapers of the period were more substantial than those of today, and many reproduced pr

23、ecise accounts of court trials and public events. Rural Canadians read magazines and books and held discussions about them at club meetings.2 Rural Canadians were also able to get together socially. The local school served other functions besides providing formal education, and school districts were

24、 often the only sign of political organization in vast regions of the country. Every community valued its one- room schoolhouse as a meeting place, especially during the winter, when work on the farm was much lighter and people had more time for a variety of social and cultural events. People of all

25、 ages got together to sing and play musical instruments, perform skits, and play parlor games.3 Between 1880 and 1920, there was a growing exodus from farms to the city, mainly because smaller farms could not afford to modernize their technology and were no longer able to support the entire family.

26、However, most Canadians continued to hold rural values, and artists and writers romanticized the family farm. In the novel Anne of Green Gables (1908), Lucy Maud Montgomery wrote about a young woman who strove to reconcile the beauty and peace of the rural landscape with the need to leave it in orde

27、r to fulfill her ambitions. For large numbers of young Canadians, growing up meant leaving the farm to find work in the city.（分数：7.00）(1).According to the passage, rural Canada in the 1880s was not an isolated wasteland because（分数：1.00）A.most farms were close to the cityB.education was inexpensiveC.

28、the rural population was growingD.information was available to farmers(2).The author makes the point that the postal service（分数：1.00）A.did not reach rural areas until the 1880sB.served an important function in rural CanadaC.provided jobs for many rural CanadiansD.was expensive to operate in rural ar

29、eas(3).Many social gatherings took place during the winter because（分数：1.00）A.there was less work to do on the farmB.there were fewer court trials or political activitiesc. social gatherings were forbidden at other timesD. many holidays occurred in the winter(4).According to the passage, the rural sc

30、hool provided all of the following services EXCEPT（分数：1.00）A.formal educationB.public health clinicsC.political organizationD.social and cultural events(5).What reason is given for large numbers of people leaving the family farm?（分数：1.00）A.There was not enough work on the farm during the winter.B.Pe

31、ople grew tired of the social isolation of rural life.C.Small farms could no longer support the whole family.D.Modern farm technology was not available in many areas.(6).Which statement best describes the period from 1880 to 1920?（分数：1.00）A.Literature portrayed a romanticized view of life on the far

32、m.B.More Canadians lived in urban areas than in rural areas.C.Rural communities began to acquire characteristics of the city.D.People gave up their rural values when they moved to the city.(7).The novel Anne of Green Gables serves to illustrate（分数：1.00）A.the need for farmers to modernize their techn

33、ologyB.the view of rural Canada as an isolated wastelandC.the importance of social connections in rural CanadaD.the experience of many young Canadians of the periodICE1 Two conditions are necessary for the formation of ice: the presence of water and temperatures below freezing. Ice in the atmosphere

34、 and on the ground can assume various forms, depending on the conditions under which water is converted to its solid state Ice that forms in the atmosphere can fall to the ground as snow, sleet, or hail. Snow is an assemblage of ice crystals in the form of flakes; sleet is a collection of frozen rai

35、ndrops, which are actually ice pellets. Hail consists of rounded or jagged lumps of ice, often in layers like the intemal structure of an onion. Ice also forms directly on the ground or on bodies of water. In North America, ice forms in late autumn, winter, and early spring. On very large bodies of

36、water, it may not form until late winter because there must be several months of low temperatures to chill such large amounts of water.2 On puddles and small ponds, ice first freezes in a thin layer with definite crystal structure that becomes less apparent as the ice thickens. On lakes large enough

37、 to have waves, such as the Great Lakes, the first ice to form is a thin surface layer of slush, sometimes called grease ice, which eventually grows into small floes of pancake ice. If the lake is small enough or the weather cold enough, the floes may freeze together into a fairly solid sheet of pac

38、k ice. Pack ice may cover the entire lake or be restricted to areas near the shore.3 Because water expands when it freezes, ice is less dense than liquid water and therefore floats rather than sinks in water. As ice floats on the surface of a lake, ocean, or river, it acts as an insulator and is thu

39、s important in maintaining the balance of the ecosystem. Without the insulating effect of floating ice sheets, surface water would lose heat more rapidly, and large bodies of water such as the Arctic Ocean and Hudson Bay might freeze up completely.（分数：9.00）(1).What condition is necessary for water i

40、n the atmosphere to change to its solid state?（分数：1.00）A.A solid cloud cover that absorbs the suns heatB.A weather forecast for snow, sleet, or hailC.A position directly above a large body of waterD.A temperature below waters freezing point(2).In paragraph 1, the author makes the point that（分数：1.00）

41、A.ice can take a variety of formsB.sleet and snow differ from iceC.in some years ice never forms at allD.ice rarely forms on the ground in cities(3).Ice that forms in the atmosphere in the form of layered lumps is known as（分数：1.00）A.snowB.pack iceC.hailD.grease ice(4).All of the following are forms

42、of ice that form on bodies of water EXCEPT（分数：1.00）A.sleetB.slushC.pancake iceD.pack ice(5).Why does ice form later on very large bodies of water?（分数：1.00）A.Most large bodies of water are located at low elevations or low latitudes.B.It takes several months of cold temperatures to cool a large body o

43、f water.C.Large bodies of water are fed by underground springs of warmer water.D.The waves on large bodies of water prevent the water from freezing quickly.(6).When ice starts to form on small bodies of water,（分数：1.00）A.it takes the shape of small floesB.it freezes more quickly in the centerC.its su

44、rface feels greasy to the touchD.its crystal structure can be seen(7).Which statement is true about pancake ice?（分数：1.00）A.It forms on puddles and small ponds.B.It falls from the atmosphere to the ground.C.It may become a sheet of pack ice.D.It is the least dense form of ic(8).Which of the following

45、 is an effect of the density of ice?（分数：1.00）A.Ice that forms on large lakes has a greasy consistency.B.Each ice crystal is unique, but all are six-sided structures.C.Pack ice is restricted to areas near the shore of a lake.D.Floating ice sheets prevent bodies of water from losing heat.(9).The passa

46、ge mentions all of the following characteristics of ice EXCEPT（分数：1.00）A.its appearanceB.where it formsC.the rate at which it meltsD.its effect on the ecosystemTHE ROLE OF GOVERNMENT IN THE ECONOMY1 Because most people do not volunteer to pay taxes or police their own financial affairs, governments

47、cannot influence economic activity simply by asking people to pollute less, to give money to the poor, or to be innovative. To accomplish these things, governments have to pass laws. Since the early twentieth century, governments of countries with advanced industrial or service economies have been p

48、laying an increasing role in economics. This can be seen in the growth of government taxation and spending, in the growing share of national income devoted to income-support payments, and by the enormous increase in the control of economic activity.2 The large-scale organization of business, as seen

49、 in mass production and distribution, has led to the formation of large-scale organizations-corporations, labor unions, and government structures-that have grown in importance in the past several decades. Their presence and growing dominance have shifted capitalist economies away from traditional market forces and toward government administration of markets.3 In the United States, government provides a framework of laws for the conduct of economic activity that attempt to make it serve the public interest. For instance, the individual states and the federal government have passed