大学英语六级分类模拟题486及答案解析.doc
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1、大学英语六级分类模拟题 486及答案解析(总分:242.00,做题时间:90 分钟)一、Part Writing(总题数:1,分数:15.00)1.1随着科技的发展,现代人的技能也随之变化 2有人认为外语、计算机等技能很重要,也有人认为沟通技能更重要 3在我看来 (分数:15.00)_二、Part Reading Compr(总题数:0,分数:0.00)三、Section A(总题数:1,分数:71.00)Petroleum ResourcesA) Petroleum, consisting of crude oil and natural gas, seems to originate fr
2、om organic matter in marine sediment. Microscopic organisms settle to the seafloor and accumulate in marine mud. The organic matter may partially decompose, using up the dissolved oxygen in the sediment. As soon as the oxygen is gone, decay stops and the remaining organic matter is preserved. B) Con
3、tinued sedimentationthe process of deposits“ settling on the sea bottomburies the organic matter and subjects it to higher temperatures and pressures, which convert the organic matter to oil and gas. As muddy sediments are pressed together, the gas and small droplets of oil may be squeezed out of th
4、e mud and may move into sandy layers nearby. Over long periods of time ( millions of years), accumulations of gas and oil can collect in the sandy layers. Both oil and gas are less dense than water, so they generally tend to rise upward through water-saturated rock and sediment. C) Oil pools are val
5、uable underground accumulations of oil, and oil fields are regions underlain by one or more oil pools. When an oil pool or field has been discovered, wells are drilled into the ground. Permanent towers, called derricks, used to be built to handle the long sections of drilling pipe. Now portable dril
6、ling machines are set up and are then dismantled and removed. 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. Although this rise of oil is almost always carefully control
7、led today, spouts of oil, or gushers, were common in the past. Gas pressure gradually dies out, and oil is pumped from the well. Water or steam may be pumped down adjacent wells to help push the oil out. At a refinery, the crude oil from underground is separated into natural gas, gasoline, kerosene,
8、 and various oils. Petrochemicals such as dyes, fertilizer, and plastic are also manufactured from the petroleum. D) As oil becomes increasingly difficult to find, the search for it is extended into more hostile environments. The development of the oil field on the North Slope of Alaska and the cons
9、truction of the Alaska pipeline are examples of the great expense and difficulty involved in new oil discoveries. Offshore drilling platforms extend the search for oil to the ocean“s continental shelvesthose gently sloping submarine regions at the edges of the continents. More than one-quarter of th
10、e world“s oil and almost one-fifth of the world“s natural gas come from offshore, even though offshore drilling is six to seven times more expensive than drilling on land. A significant part of this oil and gas comes from under the North Sea between Great Britain and Norway. E) Of course, there is f
11、ar more oil underground than can be recovered. It may be in a pool too small or too far from a potential market to justify the expense of drilling. Some oil lies under regions where drilling is forbidden, such as national parks or other public lands. Even given the best extraction techniques, only a
12、bout 30 to 40 percent of the oil in a given pool can be brought to the surface. The rest is far too difficult to extract and has to remain underground. F) Moreover, getting petroleum out of the ground and from under the sea and to the consumer can create environmental problems anywhere along the lin
13、e. Pipelines carrying oil can be broken by faults or landslides, causing serious oil spills. Spillage from huge oil-carrying cargo ships, called tankers, involved in collisions or accidental groundings (such as the one off Alaska in 1989) can create oil slicks at sea. Offshore platforms may also los
14、e oil, creating oil slicks that drift ashore and foul the beaches, harming the environment. Sometimes, the ground at an oil field may subside as oil is removed. The Wilmington field near Long Beach, California, has subsided nine meters in 50 years; protective barriers have had to be built to prevent
15、 seawater from flooding the area. Finally, the refining and burning of petroleum and its products can cause air pollution. Advancing technology and strict laws, however, are helping control some of these adverse environmental effects. G) Natural gas is a naturally occurring hydrocarbon gas mixture c
16、onsisting primarily of methane, but commonly includes varying amounts of other higher alkanes and even a lesser percentage of carbon dioxide, nitrogen, and hydrogen sulfide. Natural gas is an energy source often used for heating, cooking, and electricity generation. It is also used as fuel for vehic
17、les and as a chemical feedstock in the manufacture of plastics and other commercially important organic chemicals. H) Natural gas is found in deep underground rock formations or associated with other hydrocarbon reservoirs in coal bedsand as methane clathrates. Petroleum is also another resource fou
18、nd in proximity to and with natural gas. I) Most natural gas was created over time by two mechanisms: biogenic and thermogenic. Biogenic gas is created by methanogenic organisms in marshes, bogs, landfills, and shallow sediments. Deeper in the earth, at greater temperature and pressure, thermogenic
19、gas is created from buried organic material. J) Before natural gas can be used as a fuel, it must undergo processing to remove impurities, including water, to meet the specifications of marketable natural gas. K) The by-products of processing include ethane, propane, butanes, pentanes, and higher mo
20、lecular weight hydrocarbons, hydrogen sulfide (which may be converted into pure sulfur) , carbon dioxide, water vapor, and sometimes helium and nitrogen. L) Natural gas is often informally referred to simply as gas, especially when compared to other energy sources such as oil or coal. M) However, it
21、 is not to be confused with gasoline, especially in North America, where the term gasoline is often shortened in colloquial usage to gas. N) In the 19th century, natural gas was usually obtained as a by-product of producing oil, since the small, light gas carbon chains came out of solution as the ex
22、tracted fluids underwent pressure reduction from the reservoir to the surface, similar to uncapping a bottle of soda where the carbon dioxide effervesces. O) Unwanted natural gas was a disposal problem in the active oil fields. If there was not a market for natural gas near the wellhead it was virtu
23、ally valueless since it had to be piped to the end user.(分数:71.00)(1).According to the analysis, there are two main parts in the petroleum, namely the crude oil and natural gas.(分数:7.10)(2).When it comes to the mechanism of petroleum, there are two kinds including the biogenic and thermogenic ones.(
24、分数:7.10)(3).After a long time, (millions of years) , accumulations of gas and oil can collect in the sandy layers.(分数:7.10)(4).Generally speaking, natural gas could be found in two areas, firstly the deep underground rock formations, and then the hydrocarbon reservoirs in coal bedsand.(分数:7.10)(5).O
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