1、考博英语模拟试卷 160及答案与解析 一、 Reading Comprehension 0 Valvular heart diseases are quite common, essentially resulting in impaired blood flow and were very difficult to treat. Some 30 years ago, it became possible to replace .diseased valves with prostheses to impose a greater control over blood flow. Early
2、devices were of the mechanical variety, in which devices like ball-in-a-cage or tilting disc would be used to allow blood to flow under near-normal conditions. Although a few mechanical problems were encountered in the early days, the major difficulty lay with the tendency for any foreign material t
3、o initiate a blood clot. So, all valve recipients have to be given anticoagulant therapy. This is not particularly desirable for the patients, who may develop bleeding problems, and in any case is not always successful. Although good results are achieved with these valves, it was considered necessar
4、y to develop alternatives and the direction was that of natural tissues. Its not possible to transplant heart valves untreated because of rejection phenomena, but it became apparent that collagenous tissue could be cross-linked by glutaraldehyde and prepared in the form of a heart valve. Two sources
5、 of tissue were considered for this purpose, bovine pericardium ( collagenous tissue derived from the wall of a cows heart) and porcine valves (heart valves taken from pigs) and the resulting “bioprosthetic valve“ appeared to be very promising. It was particularly important that these patients didnt
6、 need anticoagulation. Unfortunately, these valves have not proved very durable, the cross-linked collagen suffering from slow calcification and deterioration so most of the replacement valves themselves need to be replaced within a decade. This would tend to suggest that the mechanical valves give
7、superior performance, notwithstanding the anticoagulation problem, and a move back towards their use might have been expected. However, most of the valves in current use incorporate an alloy( usually Stellite) for the housing, and a carbon coated occuluder. The complex shapes of some of the housing
8、have required combinations of casting and welding technologies to be used in their construction and serious problems have arisen with a valve design from one manufacturer, where a small number of catastrophic fractures have occurred within the housing. In patients where this valve has been used to t
9、reat aortic valve disease, this fracture is usually fatal and although the risks are small, the problem is important to the industry. Also, at a time when this dichotomy is exercising the minds of surgeons, scientists and regulatory bodies alike, the emergence of the disease BSE in cattle has placed
10、 even further restrictions on the use of animal tissue for this type of application and the whole question of prosthetic heart valves has been turned from a reasonable successful example of reconstructive implant surgery to a very confused area. This serves to highlight some of the very varied probl
11、ems of facing the use of biomaterials. 1 This passage is extracted from an article written by an expert on _. （ A） surgical equipment （ B） heart diseases （ C） materials for surgical implants （ D） mechanical valve manufacturing 2 What does “this dichotomy“ in last paragraph refer to? （ A） Cows heart
12、wall or pigs heart valve. （ B） Tissues or device. （ C） Housing or occuluder. （ D） Anticoagulation or calcification. 3 Which of the following can be classified as a mechanical valve? （ A） Tilting disc device. （ B） Aortic valve. （ C） Collagenous tissue. （ D） Porcine valve. 4 Which of the following doe
13、s nut need to he considered in the area of heart valve replacement? （ A） Rejection phenomena. （ B） Anticoagulation. （ C） Durability. （ D） Regulatory bodies. 5 Which of the following is not mentioned in the passage? （ A） The causes of BSE. （ B） The quality of the artificial valve. （ C） The result of
14、failure of the valves of the heart. （ D） The way to make valve with animal tissue. 5 Water will evaporate from any wetted surface. A .significantly large fraction of the rainfall that falls on land is returned to the atmosphere in this fashion. In addition water is assimilated by root systems of gro
15、wing plants and is later transpired from the leaf surfaces by a process essentially identical to evaporation. The two effects, evaporation and transpiration, cannot be individually discriminated for their effectiveness in returning rainfall to the atmosphere, but their sum contribution can be evalua
16、ted and is usually called the evapotranspiration factor. The fraction of rain falling on the United States that is returned to the atmosphere by evapotranspiration, for example, is 70 percent; for the world as a whole, approximately 62 percent. In arid countries such as Australia the fraction is lar
17、ger, and in less arid areas such as the United Kingdom it is lower. Water returned to the atmosphere by evapotranspiration is unavailable to man, except in, the sense that useful plants may be grown in the place of useless ones. It cannot be trapped and redistributed for industrial or other purposes
18、. In regions of low rainfall, plant cover will develop to a point where all precipitation is used in evapotranspiration and none remains for stream now. Seasonal rainfalls provide a qualifier for this statement because streams will flow even in the most arid areas during periods of maximum rainfall.
19、 In general, if the potential evapotranspirationthat which would result from the maximum plant cover a region could support under ideal circumstancesshould exceed the precipitation, overland stream flow ceases. Conversely, if evapotranspiration is less than precipitation, runoff is generated. The am
20、ount by which precipitation exceeds evapotranspiration is the perennial yield of stream flow water, and this is the usable fraction of rain and snowfall. Across the entire United States the water yield amounts to 30 percent of the total rainfall, or approximately 1.771015 liters per year. But when w
21、e consider the distribution of water deficiencies and surpluses we find that essentially the entire eastern half of the United States, together with a small region in the Pacific northwest, enjoys water surplus, while most of the country to west of the Mississippi is water- deficient and arid. 6 Acc
22、ording to the passage, a greater fraction of rainfall on the globe we live comes from_. （ A） the evaporated and transpired water from the earth itself （ B） the wet atmosphere above in the sky （ C） returning rainfall to the atmosphere （ D） the mixture of wet and dry air 7 If the amount of evaporated
23、water is less than the amount of water falling on, then _. （ A） stream flow will appear （ B） the surplus of water will run off （ C） flood will be generated （ D） the plant has to transpire the surplus 8 Which of the following is true? （ A） Water evaporated to atmosphere is unavailable to man because
24、it is from useless plants. （ B） Man can interfere with water evaporation by growing some plants. （ C） Man can recycle evaporated water to grow useful plants. （ D） Useful plants can collect the evaporated water which will be used for other purpose. 9 According to the passage, the water that is availa
25、ble to us is _. （ A） equal to the precipitation （ B） purified by useful plants （ C） the fraction of water that is not evaporated （ D） the rain falling and the snow melted 10 It can be inferred from the passage that _. （ A） more than 30% of total rainfall can yield stream flow in the United States （
26、B） the water in the entire eastern haft of U. S.A. goes beyond its necessary need （ C） west part of U. S. A.doesnt have perennial yield of stream flow water （ D） the yield of stream flow water is unevenly distributed in the United States 10 Aids in South Africa is threatening to become a problem. At
27、 the end of 1993, 4.25% of South African adults were HIV positive. By the end of 1994, the figure was 7.57%. This increase in a year is the largest for the spread of the virus in Africa and possibly the world, and it seems certain that 12% or more of the population will be HIV positive by Christmas.
28、 In the worst hit area, the HIV positive rate now tops 20%. It seems South Africa is moving rapidly towards the catastrophic 35% levels of infection in East Africa. This will be the first time that the virus will have become so widespread in a sophisticated, industrialized country. Both the present
29、and preceding governments should bear responsibility; each was aware of the crisis and did almost nothing. There is no public campaign to promote safe sex, for example. The apartheid regime was too conscious of religious sensitivities to organize an explicit anti-Aids campaign, and the African Natio
30、nal Congress is far too nervous about traditional African attitudes to sex. A survey of black women in Johannesburg revealed that 75% were willing to accept condoms if they could persuade their partners to use them, but that in practice only 2% had managed to do so. Women are the chief victims with
31、the highest HIV-positive rates among nurses and teachers. Many African men have responded to the epidemic by choosing younger and younger partners. There is even a myth that sex with a young enough girl can cure an Aids-stricken male. Inevitably young women are the hardest hit, a phenomenon compound
32、ed by the high incidence of rape. More than 100 rapes are reported to the authorities every day, although this figure is believed to represent a minority of actual cases. Despite the spread of the virus, the statistics manage to struggle on to only about page six of most South African newspapers bec
33、ause the crisis is still in “phoney war“ stage although there are more than 1.8 million HIV-positive South Africans, relatively few of them have developed Aids. Doctors say the virus seems to be taking longer to move through its cycle here, perhaps because South Africans with their higher standards
34、of living, are healthier and therefore more resistant than people further north in Africa. Without doubt, the present air of complacency will vanish as soon as high profile members of the elite begin to be affected and the implications for the economy sink in. Moreover, the spread of the virus may g
35、reatly damage the present racial reconciliation in South Africa, since Aids is now overwhelmingly a disease of blacks, and many whites are beginning to see almost every African as an Aids risk. 11 According to the passage, which of the following is not blamed as the factor that prevents anti- Aids c
36、ampaign? （ A） Over sensitive to religious belief. （ B） Traditional African attitude to sex. （ C） High standard of living. （ D） The myth about having intercourse with a virgin. 12 It is suggested in the passage that _. （ A） Aids case is rare in highly advanced countries （ B） South Africa has the high
37、est Aids rate in the world （ C） the press tried to report a phoney war （ D） minority young women are more often raped 13 Which group of the following people tends to have highest rate of Aids? （ A） The black elite. （ B） Women not using condoms. （ C） Aids-stricken black male. （ D） Young black women.
38、14 What does “the statistics manage to struggle on to only about page six of most South African newspapers“ imply? （ A） Page six of most South African newspapers usually carries important stories. （ B） The issue concerned has not been boosted to the top of public attention. （ C） Its hard to establis
39、h statistics on page six of South African newspapers. （ D） Not many of positive persons developed Aids. 15 According to the passage, with the increasing rate of Aids, _. （ A） people on the top of the social ladder cant escape the infection （ B） people will continue to be complacent （ C） people will
40、realize the consequences brought to economy （ D） whites will alienate the black more 15 When I became president of the University of Michigan, affirmative action in higher education was under siege. Buoyed by a successful lawsuit against the University of Texas law schools admission policy and by ba
41、llot initiatives such as Californias Proposition 209, which outlawed race as a factor in college admissions, the opponents set their sights on affirmative-action programs at college across the country. The rumor that Michigan would be the next target in this campaign turned out to be correct. I beli
42、eved strongly that we had no choice but to mount the best legal defense ever for diversity in higher education and take special efforts to explain this complex issue, in simple and direct language, to the American public. There are many mispereeptions about how race and ethnieity are considered in c
43、ollege admissions. Competitive colleges and universities are always looking for a mix of students with different experiences and backgrounds academic, geographic, international, socioeconomic, athletic, public-service oriented, and, yes, racial and ethnic. It is true that in sorting the initial rush
44、 of applications, large universities will give “points“ for various factors in the selection process in order to ensure fairness as various officers review applicants. Opponents of Michigans undergraduate system complain that an applicant is assigned more points for being black, Hispanic, or Native
45、American than for having a perfect SAT score. This is true, but it trivializes the real issue: whether, in principle, race and ethnicity are appropriate considerations. The simple fact about the Michigan undergraduate policy is that it gives overwhelming weight to traditional academic factors some 1
46、10 out of a total of 150 points. After that, there are some 40 points left for other factors, of which 20 can be allocated for race or socioeconomic status. Race has been a defining element of the American experience. The historic Brown v. Board of Education decision is almost 50 years old, yet metr
47、opolitan Detroit is more segregated now than it was in 1960. The majority of students who each year arrive on a campus like Michigan graduated from virtually all-white or all-black high schools. The campus is their first experience living in an integrated environment. Diversity is not merely a desir
48、able addition to a well-rounded education. It is as essential as the study of the Middle Ages, of international politics, and of Shakespeare. For our students to better understand the diverse country and world they inhabit, they must be immersed in a campus culture that allows them to study with, ar
49、gue with, and become friends with students who may be different from them. It broadens the mind, and the intellect-essential goals of education. Reasonable people can disagree about affirmative action. But it is important that we do not lose the sense of history, the compassion and the largeness of vision that defined the best of the civil-rights era, which has given rise to so much of what is good about America today. 16 This passage is mainly_. （ A） explanative （ B） descriptive （ C） argumentative （ D） narrative 17 Whats th
