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冲分救命题 -8369【medium】 00:00:00 关闭计时
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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?


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。
1楼  | 2021-05-02 19:48:55 回复
  • 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
    2021-05-02 19:50:37 回复
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