1、大学英语六级改革适用（阅读）模拟试卷 34及答案与解析 Section C 0 The fertile land of the Nile delta is being eroded along Egypts Mediterranean coast at an astounding rate, in some parts estimated at 100 metres per year. In the past, land scoured away from the coastline by the currents of the Mediterranean Sea used to be rep
2、laced by sediment brought dawn to the delta by the River Nile, but this is no longer happening. Up to now, people have blamed this loss of delta land on the two large dams at Aswan in the south of Egypt, which hold back virtually all of the sediment that used to flow down the river. Before the dams
3、were built, and the Nile flowed freely, carrying huge quantities of sediment north from Africa s interior to be deposited on the Nile delta. This continued for 7,000 years, eventually covering a region of over 22,000 square kilometres with layers of fertile silt. Annual flooding brought in new, nutr
4、ient-rich soil to the delta region, replacing what had been washed away by the sea, and dispensing with the need for fertilizers in Egypt s richest food-growing area. But when the Aswan dams were constructed in the 20th century to provide electricity and irrigation, and to protect the huge populatio
5、n centre of Cairo and its surrounding areas from annual flooding and drought, most of the sediment with its natural fertilizer accumulated up above the dam in the southern, upstream half of Lake Nasser, instead of passing down to the delta. Now, however, there turns out to be more to the story. It a
6、ppears that the sediment-free water emerging from the Aswan dams picks up silt and sand as it erodes the river bed and banks on the 800-kilometre trip to Cairo. Daniel Jean Stanley of the Smithsonian Institute noticed that water samples taken in Cairo, just before the river enters the delta, indicat
7、ed that the river sometimes carries more than 850 grams of sediment per cubic metre of water almost half of what it carried before the dams were built. “Im ashamed to say that the significance of this didnt strike me until I had read 50 or 60 studies,“ says Stanley in Marine Geology. “There is still
8、 a lot of sediment coming into the delta, but virtually no sediment comes out into the Mediterranean to replenish the Coastline. So this sediment must be trapped on the delta itself.“ According to Siegel, international environmental organizations are beginning to pay closer attention to the region,
9、partly because of the problems of erosion and pollution of the Nile delta, but principally because they fear the impact this situation could have on the whole Mediterranean coastal ecosystem. But there are no easy solutions. In the immediate future, Stanley believes that one solution would be to mak
10、e artificial floods to flush out the delta waterways, in the same way that natural floods did before the construction of the dams. He says, however, that in the long term an alternative process such as desalination may have to be used to increase the amount of water available, “In my view, Egypt mus
11、t devise a way to have more water running through the river and the delta,“ says Stanley. Easier said than done in a desert region with a rapidly growing population. 1 Why is the fertile land of the Nile delta being eroded? （ A） Because some chemicals corroded the land. （ B） Because the land has bee
12、n deserted for a long time. （ C） Because acid rain eroded the land. （ D） Because land cleaned away from the coastline by the currents of the Mediterranean Sea cannot be refilled by sediment. 2 The Nile delta didn t need fertilizers because_. （ A） the Nile carried huge quantities of sediment from Afr
13、ica to be deposited on the Nile delta （ B） annual flooding washed away fertile silt （ C） the soil itself contained large quantity of nutrition （ D） annual flooding brought in new, nutrient-rich soil to the delta region 3 Which of the followings is not a purpose for the construction of Aswan dams? （
14、A） To provide electricity. （ B） To supply irrigation water. （ C） To promote shipping industry. （ D） To protect Cairo and its surrounding areas from annual flooding. 4 What does Stanley find out about the real effect of the Aswan dams? （ A） The sediment replenishes the Mediterranean coastline. （ B） T
15、he sediment must be left on the delta. （ C） The dams causes frequent landslides. （ D） The dams destroyed the ecosystem of the area. 5 In the long run, what is a possible solution to the problem of the erosion of the Nile delta? （ A） A method such as desalination to increase the amount of water avail
16、able. （ B） A way to make artificial floods to flush out the delta waterways. （ C） A method which takes the whole Mediterranean coastal ecosystem into consideration. （ D） A pollution of the Nile delta. 5 A number of scientific studies have found that the amount of sugar we consume is a major factor i
17、n how big Americans have become. In the last half-century, consumption of sugars by the average American has increased by more than 24 pounds a year, expanding waistlines and crowding out more nutritious foods. Furthermore, the studies indicate that the main dietary culprit(罪魁祸首 )for both the increa
18、se in sugar and the weight of Americans has been the ever-growing consumption of sugary drinks, especially soda. These soft drinks contribute 7 percent of the calories Americans consume, making them the leading source of added sugar and the single largest source of calories in our diet. Critics have
19、 repeatedly blamed high-fructose corn syrup, the inexpensive sweetener that has helped to keep soda prices down and allowed consumption to soar. But in fact, no sugary beverage and no caloric sweetener are blameless. Not ordinary table sugar; not brown sugar or raw sugar; not honey; not even fruit j
20、uice concentrate. All these sweeteners when added to drinks contribute mostly empty calories that do little to satisfy the appetite and end up as excess energy that the body ultimately turns to fat. And soda, though the most common sugary beverage, is not the only one involved. In fact, after decade
21、s of increases, soda consumption has levelled off, but sports drinks, energy drinks and sweetened teas have become increasingly important contributors to the liquid calories Americans consume. To improve the health of its residents and its coffers, New York State is considering a consumption tax of
22、about one penny per ounce on high-calorie sweetened beverages. The American Beverage Association, which takes major credit for an 88 percent reduction in sugared soda calories in the nation s schools, has seriously undermined its credibility with ads opposing the so-called soda tax. In association-s
23、ponsored commercials on television and radio, housewives spout the ridiculous argument that such a tax would make it more difficult for them to feed their families. But on no nutritionist s list are you likely to find soda listed as a desirable dietary ingredient. It is not a food, nor a basic neces
24、sity. In fact, the people likely to benefit most from a soda tax that discourages consumption are those who find it hardest to make ends meet. These are the people who can least afford to waste hard-earned dollars on empty calories that undermine their health. 6 1.What have many studies found accord
25、ing to the first two paragraphs? （ A） Americans diet contains too many nutritious foods. （ B） Soda is one major contributor to Americans overweight. （ C） Americans diet has the largest number of calories. （ D） Americans consume the most sugars in the world. 7 What can we know about the empty calorie
26、s from the passage? （ A） They make people have no appetite. （ B） They are the main source of Americans energy. （ C） They are Americans basic necessity. （ D） They are bad for people s health. 8 What measure does New York State want to take to improve its people s health? （ A） It is planning to impose
27、 taxes on sugary drinks with high calories. （ B） It is considering limiting the amount of liquid calories Americans consume. （ C） It limits the amount of sugar added to the sugary drinks. （ D） It encourages the sellers to raise the price of the drinks with high calories. 9 Why did the American Bever
28、age Association lose its credibility? （ A） It did not think all the sugary drinks were harmful. （ B） It opposed to reducing its nation schools soda calories. （ C） It did not support the so-called soda tax. （ D） It discouraged people to consume soda drinks. 10 What is housewives attitude towards the
29、soda tax? （ A） Indifferent. （ B） Supporting. （ C） Suspicious. （ D） Disapproving. 10 The molecules of carbon dioxide in the Earth s atmosphere affect the heat balance of the Earth by acting as a one-way screen. Although these molecules allow radiation at visible wavelengths, where most of the energy
30、of sunlight is concentrated, to pass through, they absorb some of the longer-wavelength, infrared emissions radiated from the Earth s surface, radiation that would otherwise be transmitted back into space. For the Earth to maintain a constant average temperature, such emissions from the planet must
31、balance incoming solar radiation. If there were no carbon dioxide in the atmosphere, heat would escape from the Earth much more easily. The surface temperature would be so much low that the oceans might be a solid mass of ice. Today, however, the potential problem is too much carbon dioxide. The bur
32、ning of fossil fuels and the clearing of forests have increased atmospheric carbon dioxide by about 15 percent in the last hundred years, and we continue to add carbon dioxide to the atmosphere. Could the increase in carbon dioxide cause a global rise in average temperature, and could such a rise ha
33、ve serious consequences for human society? Mathematical models that allow us to calculate the rise in temperature as a function of the increase indicate that the answer is probably yes. Under present conditions, a temperature of -18 can be observed at an altitude of 5 to 6 kilometres above the Earth
34、. Below this altitude(called the radiating level), the temperature increases by about 6 per kilometre approaching the Earth s surface, where the average temperature is about 15 . An increase in the amount of carbon dioxide means that there are more molecules of carbon dioxide to absorb infrared radi
35、ation. As the capacity of the atmosphere to absorb infrared radiation increases, the radiating level and the temperature of the surface must rise. One mathematical model predicts that doubling the atmospheric carbon dioxide would raise the global mean surface temperature by 2.5 . This model assumes
36、that the atmospheres relative humidity remains constant and the temperature decreases with altitude at a rate of 6.5 per kilometre. The assumption of constant relative humidity is important, because water vapour in the atmosphere is another efficient absorber of radiation at infrared wavelengths. Be
37、cause warm air can hold more moisture than cool air, the relative humidity will be constant only if the amount of water vapour in the atmosphere increases as the temperature rises. Therefore, more infrared radiation would be absorbed and reradiated back to the Earths surface. The resultant warming a
38、t the surface could be expected to melt snow and ice, reducing the Earth s reflectivity. More solar radiation would then be absorbed, leading to a further increase in temperature. 11 According to the passage, the greatest part of the solar energy that reaches the Earth is_. （ A） concentrated in the
39、infrared spectrum （ B） concentrated at visible wavelengths （ C） absorbed by carbon dioxide molecules （ D） absorbed by atmospheric water vapour 12 According to the passage, which of the following is true of the last hundred years? （ A） Fossil fuels were burned for the first time. （ B） Greater amounts
40、 of land were cleared than at any time before. （ C） The average temperature at the Earth s surface has become 2C cooler. （ D） The amount of carbon dioxide in the atmosphere has increased measurably. 13 Which of the following best describes the authors attitude toward the increasing amount of carbon
41、dioxide in the atmosphere and its consequences? （ A） Incredulous. （ B） Completely detached. （ C） Objective yet concerned. （ D） Angry yet resigned. 14 It can be concluded from information contained in the passage that the average temperature at an altitude of 1 kilometre above the Earth is_. （ A） 15C
42、 （ B） 9C （ C） 2.5C （ D） -12C 15 It can be inferred from the passage that the construction of the mathematical model mentioned in the passage involved the formulation of which of the following? （ A） An assumption that the amount of carbon dioxide added to the atmosphere would in reality steadily incr
43、ease. （ B） An assumption that human activities are the only agencies by which carbon dioxide is added to the atmosphere. （ C） Assumptions about the social and political consequences of any curtailment of the use of fossil fuels. （ D） Assumptions about the physical conditions that are likely to preva
44、il during the period for which the model was made. 15 You ve been working out regularly for quite a while, but you re nowhere near your fitness goals. So now it s time to bring in your ultimate weapon your mind. Rather than thinking of fitness as something mysterious that you do with your body, take
45、 an analytical, goal-oriented approach to making physical improvements that stick. Try these tips for creating a smart fitness plan: Define your goals. Whether it s to lose fat and gain muscle or to run a triathlon, it s vital to have a goal to work toward. Knowing where youre going makes it easier
46、to take the right steps. Get realistic. Training gains are met through consistent effort over a period of time. Dont expect dramatic, overnight results regardless of what exercise equipment infomercials claim. Reward yourself for all the little positive steps you take and for consistently striving f
47、orward. Be yourself. Work toward a goal that you can achieve with your body. Don t try to change your basic shape or to go against your own unique physical capabilities. Take an objective look at yourself, and then work toward enhancing what youve got rather than trying to attain someone else s body
48、. Do your research. If you are not making progress, ask a qualified personal trainer to analyze your routine and your goals. Read health and fitness magazines. There s tons of great fitness information out there tailor it to fit you. Identify your weaknesses, and then use your brain to outsmart them
49、. Many people avoid their weak points or bad habits, hoping that they can ignore them into oblivion. Instead, take them up as clues to how you can improve. Keep a food and fitness journal for a month. Then analyze it for negative patterns. If you always overeat late at night, try going to a late-night movie to get your mind off food. If you tend to fade out on your workouts on weekends, plan some fun exercise with friends to spice up your lagging routine. Create a fitness network. Integrate the important people in your li
