The passage suggests which of the following about air pollution?答案解析-雷哥GRE

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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, and ozone (generated by photochemical reactions with hydrocarbons 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 a massive shift away from the private automobile—is to replace conventional diesel fuel and gasoline with cleaner-burning fuels such as compressed natural gas, liquefied petroleum gas, 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 any, 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 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 improvements that methanol makes feasible would still contribute to an immediate lessening of urban air pollution.

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. (E) Reductions in pollutants emitted by individual vehicles have been offset by increases in pollution from sources other than gasoline fueled vehicles.

正确答案： A 耗时：

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399621qnson

题干没有可定位信息，只能⽤选项定位。A选项可依据⾸段：There is a growing realization that the only effective way to achieve further reductions in vehicle emissions……只能采⽤替代性燃料，说明传统燃料没有提⾼空间了。

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2021-05-02 19:48:55

399621qnson 回复 399621qnson
B. 减 gasoline 的措施效果很失败呀。不对，第一段第一句说了这几年有 substantial reduction，后面要做的是 further reduction。 C. 为减排我们还没做过啥事。不对，起码减少 gasonline 这件事肯定做了。 D. gasonline 引起的污染不是最 critical 的。按照文章从上到下一层层的逻辑，gasoline 应该是最 critical 的吧，毕竟它最早被批斗得一无是处，其它燃料都只是有一部分局限性。就算不是最 critical，文章作者起码也没有暗示这一点。 E. vehicles 减少的污染被那些非 gasoline 的

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2021-05-02 19:50:37

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