首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Although recent years have seen substantial reductions in noxious pollutants from individual motor vehicles, the number of such
Although recent years have seen substantial reductions in noxious pollutants from individual motor vehicles, the number of such
admin
2015-01-31
35
问题
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 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 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 possibly 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-fuelled vehicles could be designed to be much more efficient than "gasoline clone" vehicles fuelled 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 author of the text is primarily concerned with______.
选项
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 favour of one solution to it
答案
C
解析
主旨题。本章第一段首先提出车辆废气的问题,然后指出实现车辆废气进一步减少而又不必大规模减少私家轿车的唯一有效途径是用清洁燃料来代替传统的柴油和汽油燃料。而在其他段落分别介绍了压缩天然气、液化石油气、乙醇和甲醇的优势和可行性。可知文章的思路是分析一个问题的可能解决方案的优势,和C选项表达一致。所以答案选C。
转载请注明原文地址:https://kaotiyun.com/show/ZFh7777K
0
大学英语六级
相关试题推荐
ImprovingthebalancebetweentheworkingpartofthedayandtherestofitisagoalofagrowingnumberofworkersinrichWe
Choiceblindness:Youdon’tknowwhatyouwant[A]Wehaveallheardofexpertswhofailbasictestsofsensorydiscriminationin
Choiceblindness:Youdon’tknowwhatyouwant[A]Wehaveallheardofexpertswhofailbasictestsofsensorydiscriminationin
Choiceblindness:Youdon’tknowwhatyouwant[A]Wehaveallheardofexpertswhofailbasictestsofsensorydiscriminationin
Althoughwealreadyknowagreatdealaboutinfluenza,itisdifficultforepidemiologists(流行病学家),whostudyinfectiousdisease,
Manyprivateinstitutionsofhighereducationaroundthecountryareindanger.Notallwillbesaved,andperhapsnotall【B1】__
A、TheU.S.government.B、YaleUniversity.C、TheSingaporegovernment.D、TheNationalUniversityofSingapore.C选项表明,本题与某一机构有关,听音
A、Husbands’salaryisprettyhigh.B、Husbandsaffordthewholepartoftheincome.C、Wivesandhusbandscangetthesamesalary.
Crash.Shatter.Boom.Crash.Shatter.Boom.Smatteringofsillydialogue.Prettygirlscreams:"Dad!"Crash.Shatter.Boom.Sill
Crash.Shatter.Boom.Crash.Shatter.Boom.Smatteringofsillydialogue.Prettygirlscreams:"Dad!"Crash.Shatter.Boom.Sill
随机试题
简述副节气门执行器的结构和工作原理。
生产出来的产品怎样在社会成员之间进行分配是属于经济问题中的( )问题。
下列哪些措施可致肥厚性心肌病杂音增强的是
患者男,28岁,因左耳间断性流脓伴听力下降3个月余入院。专科检查:左外耳道可见少量脓性分泌物,混有血液,性质黏稠,左耳鼓膜紧张部可见一米色肉芽沿鼓膜穿孔伸展于外耳道。耳部局部用药的描述,正确的是
期间一般分为( )。
1平方米面积上均匀垂直作用于1牛顿力所形成的压强,称之为()。
关于尾矿溢洪道施工质量,要求正确的是()。
某工程项目进展到第10周后,对前9周的工作进行了统计检查,有关统计情况见表1.问题:计算9周末的费用绩效指数CPI与进度绩效指数SPI(计算结果小数点后面保留3位),并对其结果含义加以说明。
某公司的经营杠杆系数为1.8,财务杠杆系数1.5,则该公司营业收入每增长1倍,就会引起每股收益增加()倍。
在我国城市中,由城市劳动者、工作单位或所在社区及国家共同筹集资金用以帮助劳动者及其亲属在遭遇疾病、残疾、失业、死亡等风险时保障其基本生活的制度是()。
最新回复
(
0
)