[外语类试卷]大学英语六级模拟试卷436及答案与解析.doc
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1、大学英语六级模拟试卷 436及答案与解析 一、 Part I Writing (30 minutes) 1 Directions: For this part, you are allowed 30 minutes to write an essay entitled On Food Safety Issues. You should write at least 150 words following the outline given below: 1. 食品安全的现状 2. 造成食品安全问题 的原因 3. 我们应该如何应对 On Food Safety Issues 二、 Part II
2、 Reading Comprehension (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 (f
3、or NO) if the statement contradicts the information given in the passage; NG (for NOT GIVEN) if the information is not given in the passage. 1 Part Reading Comprehension (Skimming and Scanning) Directions: In this part, you will have 15 minutes to go over the passage quickly and, answer the question
4、s on Answer Sheet 1. For questions 1-7, choose the best answer from the four choices marked A), B), C) and D). For questions 8-10, complete the sentences with the information given in the passage. Natural-gas Vehicles Kermit the Frog once said,“ Its not that easy being green. “Although he wasnt refe
5、rring to cars, his observation seems particularly appropriate for the auto industry today: designing, developing and marketing “green“ cars has not been an easy task, which is why gasoline-powered vehicles still rule the world and fossil fuels still account for almost 75 percent of the worlds energy
6、 consumption. As gasoline soar and concern over harmful emission mounts, 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
7、 cost of ownership. Natural gas basics The word“ gas“ is a confusing 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
8、liquid mixture of compounds formed underground by the decay of ancient marine animals. Natural gas also comes from the decay of ancient organisms, but it naturally takes a gaseous form instead of a liquid form. Natural gas commonly occurs in association with crude oil. It is derived from both land p
9、lants and aquatic (水生的 ) organic matter and forms above or below oil deposits. 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
10、methane (沼气 ) and other hydrocarbon gases. Hydrocarbons are organic compounds composed only of the elements carbon and hydrogen. The hydrocarbons in natural gas are called saturated hydrocarbons (饱和烃 ) because they contain hydrogen and carbon bound together by single bonds. Like gasoline, natural ga
11、s is combustible (易燃的 ) ,which means it can be used in a combustion engine like 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 modem well, equipp
12、ed with diamond-studded drill bits, can drill to depths approaching 25,000 feet. 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 p
13、ossible to transport gas miles from the source. Improvements in pipeline technology 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 natu
14、ral gas a viable energy source for many applications. The oil shortages of the 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
15、 United States. Honda also offers a personal natural gas pump to people who purchase 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-powere
16、d vehicles. In other words, the fuel ( natural gas in this case) is mixed with air in the cylinder of a four-stroke 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 flammability and ignition t
17、emperatures, NGVs themselves operate on the same fundamental concepts as gasoline-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
18、 is that they reduce environmentally harmful emissions. Natural-gas vehicles 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.
19、NGVs also rate higher in particulate matter 10 (PM10) emissions. PM10 particles transport and deposit toxic materials through the air. NGVs that operate in diesel applications can reduce PM10 emissions by a factor of 10. Natural-gas vehicles also offer these benefits: NGVs are safer. The fuel storag
20、e tanks on an NGV are thicker and stronger than gasoline or diesel tanks. There 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 conveni
21、ent and abundant.-A well-established, pipeline infrastructure exists in the 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 exhibi
22、ted significant stability compared to oil prices. Historically, natural gas 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
23、 burns so cleanly, it results in less wear and tear on the engine and extends 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 accommo
24、date the fuel storage cylinders. Not only that, these cylinders can be expensive 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 t
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