GRE阅读高频机经原文及答案汇总
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GRE阅读高频机经原文及答案：乙醇汽油
1. 乙醇汽油 1993年04月
Although, recent years have seen substantial reductions in noxious pollutants from individual motor vehicles, the number of such vehicles has been steadily increasing, consequently, more than 100 cities in the United States still have levels of carbon monoxide, particulate matter (particulate matter: 颗粒物质), and ozone (generated by photochemical reactions with hydrocarbons (hydrocarbon：n.烃, 碳氢化合物) from vehicle exhaust) that exceed legally established limits. There is a growing realization that the only effective way to achieve further reductions in vehicle emissions—short of (short of: adv.缺乏,只要没有) a massive shift away from (away from: 远离) the private automobile—is to replace conventional diesel fuel and gas
oline with cleaner-burning fuels such as compressed natural gas, liquefied petroleum gas (liquefied petroleum gas: n.液化石油气a compressed gas that consists of flammable hydrocarbons (as propane and butane) and is used especially as fuel or as raw material for chemical synthesis), ethanol, or methanol.
All of these alternatives are carbon-based fuels whose molecules are smaller and simpler than those of gasoline. These molecules burn more cleanly than gasoline, in part because they have fewer, if and, carbon-carbon bonds, and the hydrocarbons they do emit are less likely to generate ozone. The combustion of larger molecules, which have multiple carbon-carbon bonds, involves a more complex series of reactions. These reactions increase the probability of incomplete combustion and are more likely to release uncombusted and photochemically active hydrocarbon compounds into the atmosphere. On the other hand, alternative fuels do have drawbacks. Compressed natural gas would require that vehicles have a set of heavy fuel tanks—a serious liability in terms of performance and fuel efficiency—and liquefied petroleum gas faces fundamental limits on supply.
Ethanol and methanol, on the other hand, have important advantages over other carbon-based alternative fuels: they have a higher energy content (energy content: 能含量; 内能) per volume and would require minimal changes in the existing network for distributing motor fuel. Ethanol is commonly used as a gasoline supplement, but it is currently about twice as expensive as methanol, the low cost of which is one of its attractive features. Methanol’s most attractive feature, however, is that it can reduce by about 90 percent the vehicle emissions that form ozone, the most serious urban air pollutant.
Like any alternative fuel, methanol has its critics. Yet much of the criticism is based on the use of “gasoline clone” vehicles that do not incorporate even the simplest design improvements that are made possible with the use of methanol. It is true, for example, that a given volume of methanol provides only about one-half of the energy that gasoline and diesel fuel do; other things being equal, the fuel tank would have to be somewhat larger and heavier. However, since methanol-fueled vehicles could be designed to be much more efficient than “gasoline clone” vehicles fueled with methanol, they would need comparatively less fuel. Vehicles incorporating only the simplest of the engine improvement
s that methanol makes feasible would still contribute to an immediate lessening of urban air pollution.
1.1 The author of the passage is primarily concerned with(文章的逻辑结构非常明显，是指出一个问题，然后讨论了多种方案，最后指向METHANOL。其实是排除了其它的方案，或者其它方案均为陪衬。这是选D的原因。C显然不对，因为文章不但讨论的各种方案的STRENGTH，更讨论了各种方案的WEAKNESS。)
(A) countering a flawed argument that dismisses a possible solution to a problem
(B) reconciling contradictory points of view about the nature of a problem
(C) identifying the strengths of possible solutions to a problem
(D) discussing a problem and arguing in favor of one solution to it(D)
(E) outlining a plan of action to solve a problem and discussing the obstacles blocking that plan
1.2 According to the passage, incomplete combustion is more likely to occur with gasoline than with an alternative fuel because
(A) the combustion of gasoline releases photochemically active hydrocarbons
(B) the combustion of gasoline involves an intricate series of reactions
react to the recent(C) gasoline molecules have a simple molecular structure
(D) gasoline is composed of small molecules.(B)
(E) gasoline is a carbon-based fuel
1.3 The passage suggests which of the following about air pollution?
(A) Further attempts to reduce emissions from gasoline-fueled vehicles will not help lower urban air-pollution levels.
(B) Attempts to reduce the pollutants that an individual gasoline-fueled vehicle emits have been largely unsuccessful.
(C) Few serious attempts have been made to reduce the amount of pollutants emitted by gasoline-fueled vehicles.
(D) Pollutants emitted by gasoline-fueled vehicles are not the most critical source of urban air pollution.(A)
(E) Reductions in pollutants emitted by individual vehicles have been offset by increases in pollution from sources other than gasoline-fueled vehicles.

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