第四题  类比题：parallel to, similar to, analogous to,

            illustrate, give an example...

第五题  methanol

第六题  methanol

首句：让步和转折的取非关系；写作对象。

第三句

作者对方案持正评价：the only effective way

主题句和结构已经明确，剩余的为论据的延伸。

第二段

首句对象没有变化，仅作对比。

后面都是平铺直叙，不用完全理解。

第三十五行  incomplete combustion

on the other hand  作转折

do have drawbacks  表示让步语气

第三段

冒号表示重复。

细节：第六十行  however  转折 让步 递进

第四段

do may have  表示让步语气

yet 进一步表示让步语气

clone=copy

第七十行  it is true that  表示让步语气  与第七十六行 however 对应

让步和转折的取非关系。

第一题

答案：C D

(C)  identifying the strengths of possible solutions to a problem

(D)  discussing a problem and arguing in favor of one solution to it

第十五课时

第1小节

Exercise Thirty-One

 

    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.