[外语类试卷]大学英语六级模拟试卷296及答案与解析.doc
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1、大学英语六级模拟试卷 296及答案与解析 一、 Part I Writing (30 minutes) 1 Directions: For this part, you are allowed 30 minutes to write a short essay entitled Social Practice. You should write at least 150 words following the outline given below: 1. 为什么要参加社会实践 ? 2. 参加社会实 践可能会产生的问题。 3. 我对社会实践的看怯。 二、 Part II Reading Com
2、prehension (Skimming and Scanning) (15 minutes) Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions attached to the passage. For questions 1-4, mark: Y (for YES) if the statement agrees with the information given in the passage; N (for NO) if th
3、e statement contradicts the information given in the passage; NG (for NOT GIVEN) if the information is not given in the passage. 1 Natural-gas Vehicles Kermit the Frog once said, “Its not that easy bein green.“ Although he wasnt referring to cars, his observation seems particularly appropriate for t
4、he auto industry today: Designing, developing and marketing “green“ cars has not been an easy task, which is why gasoline-powered vehicles still rule the mad and fossil fuels still account for almost 75 percent of the words energy consumption. As gasoline soar and concern over harmful emission mount
5、s, however, cars that run on alternate fuel sources will become increasingly important. A natural-gas vehicle, or NGV, is the perfect example of such a car - its fuel- efficient, environmentally friendly and offers a relatively low cost of ownership. Natural Gas Basics The word “gas“ is a confusing
6、term because it is used to describe many different substances that are similar but not exactly the same. For example, the “gas“ you put in your car is gasoline, one component of crude oil, or petroleum. Petroleum is a dark, sticky liquid mixture of compounds formed underground by the decay of ancien
7、t marine animals. Natural gas also comes from the decay of ancient organisms, but it naturally takes a gaseous form instead of a liquid from. Natural gas commonly occurs in association with crude oil. It is derived from both land plants and aquatic(水生的 )organic matter and forms above or below oil de
8、posits. It is often dissolved in crude oil at the high pressures existing in a reservoir. There are also reservoirs of natural gas, known as non-associated gas, that contain only gas and no oil. Natural gas consists primarily of methane (沼气 )and other hydrocarbon gases. Hydrocarbons are organic comp
9、ounds composed only of the elements carbon and hydrogen. The hydrocarbons in natural gas are called saturated hydrocarbons because they contain hydrogen and carbon bound together by single bonds. Like gasoline, natural gas is combustible (易燃的 ), which means it can be used in a combustion engine like
10、 gasoline. But cars that could burn natural gas didnt appear on the scene until the 1930s. From Field to Ford We extract natural gas trapped in underground reservoirs by drilling wells into the earth. A modern well, equipped with diamond-studded drill bits, can drill to depths approaching 25,000 fee
11、t. Throughout the 19th century, the use of natural gas remained localized because there was no way to transport large quantities of gas over long distances. In 1890, the invention of a leakproof pipeline coupling made it possible to transport gas miles from the source. Improvements in pipeline techn
12、ology continued over the next two decades until long-distance gas transmission became practical. From 1927 to 1931, laborers constructed more than 10 major natural gas transmission systems in the United States, making natural gas a viable energy source for many applications. The oil shortages of the
13、 late 1960s and early 1970s brought renewed interest in natural gas as a fuel source, especially for automobiles. Today, owners of natural-gas vehicles can fill up their cars at one of 1,300 fueling stations located in the United States. Honda also offers a personal natural gas pump to people who pu
14、rchase its natural-gas- powered Civic. The pump uses a homes existing natural gas lines and can be installed for $ 500 to $ 1, 500. Natural-gas Vehicle Design Natural-gas vehicles use the same basic principles as gasoline-powered vehicles. In other words, the fuel ( natural gas in this case) is mixe
15、d with air in the cylinder of a four-storke engine and then ignited by a spark plug to move a piston(活塞 ) up and down. Although there are some differences between natural gas and gasoline in terms of flamability and ignition temperatures NGVs themselves operate on the same fundamental concepts as ga
16、soline-powered vehicles. Still, some modifications are required to make an NGV work efficiently. These changes are primarily in the fuel storage tank, the engine and the chassis(底盘 ). Advantages The biggest advantage of NGVs is that they reduce environmentally harmful emissions. Natural-gas vehicles
17、 can achieve up to a 93 percent reduction in carbon monoxide emissions, 33 percent reduction in emissions of various oxides of nitrogen and a 50 percent reduction in reactive hydrocarbons when compared to gasoline vehicles. NGVs also rate higher in particulate matter 10 (PM10) emissions. PM10 partic
18、les transport and deposit toxic materials through the air. NGVs that operate in diesel applications can reduce PMI0 emissions by a factor of 10. Natural-gas vehicles also offer these benefits: NGVs are safer. The fuel storage tanks on an NGV are thicker and stronger than gasoline or diesel tanks. Th
19、ere has not been an NGV fuel-tank rupture in more than two years in the United States. Natural gas costs are lower than gasoline. On average, natural gas costs one-third less than gasoline at the pump. Natural gas is convenient and abundant, A well-established, pipeline infrastructure exists in the
20、United States to deliver natural gas to almost every urban area and most suburban areas. There are more than 1,300 NGV fueling stations in the United States, and more are being added every day. Natural gas prices have exhibited significant stability compared to oil prices. Historically, natural gas
21、prices have exhibited significant price stability compared to the prices of petroleum-based fuels. This stability makes it easier to plan accurately for long-term costs. NGVs have lower maintenance costs. Because natural gas burns so cleanly, it results in less wear and tear on the engine and extend
22、s the time between tune-ups and oil changes. Disadvantages One of the biggest complaints about NGVs is that they arent as roomy as gasoline cars, This is because NGVs have to give up precious cargo and trunk space to accommodate the fuel storage cylinders. Not only that, these cylinders can be expen
23、sive to design and build - a contributing factor to the higher overall costs of a Natural-gas vehicle compared to a gasoline-powered car. Another drawback is the limited driving range of NGVs, which is typically about half that of a gasoline-powered vehicle. For example, Hondas natural gas Civic, th
24、e Civic GX, can go up to 220 miles without refueling. A typical gasoline-Powered Civic can go approximately 350 miles without refueling. If a dedicated NGV ran out of fuel on the road, it would have to be towed to the owners home or to a local natural gas refueling station, which might be harder to
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