课后练习：

1.Althoughrecent yearshave seen ______ reductions in noxiouspollutantsfrom individual motorvehicles, the number of such vehicles has been steadily increasing.

A. substantial B. substance C. submit D. subjective

2.Consequently, morethan 100 cities in the United States still have levels of carbon monoxide,particulate matter, and ozone that _____ legallyestablishedlimits.

A. succeed B. proceed C. exceed D. excess

3. There is a growingrealization that the only effective way to achieve further reductions invehicle _____ is toreplaceconventionaldiesel fuel and gasolinewithcleaner-burning fuels.

A. permission B. emission C. omission D. mission

4. All of these alternativesare carbon-based fuels _______ molecules are smaller and simpler than those ofgasoline.

A. which B. who C. what D. whose

5. The hydrocarbons theydoemit are less likely to _____ ozone.

A. generate B generous C generation D general

6. The combustion of largermolecules, _____ have multiple carbon-carbon bondsinvolvesa morecomplex series of reactions.

A. whose B. where C. who D. which

7. These reactions increase theprobability of incomplete combustion and are more likely to _____ uncombustedand photochemically active hydrocarbon compounds into the atmosphere.

A. lease B.release C. please D. relief

8. On the other hand,alternative fuels do have _____.

A. drawbacks B. setback C. drawer D. backward

9. Ethanol and methanol haveimportant advantages _____ other carbon-based alternative fuels.

A. on B. over C. by D. with

10. It is currently about______ as methanol.

A. twice as expensive as B. as twice expensive as

C. asexpensive twice as D. expensive as twice as

11. Methanol's most attractivefeature is that it can reduce _______ about 90 percent the vehicle emissions.

A. of B. in C. on D. by

12. However, sincemethanol-fueled vehicles could be designed to be much more ______ than gasolineclone vehicles fueled with methanol, they would need comparatively less fuel.

A. effective B. efficient C. sufficient D. supplement

13.Vehicles ____ only the simplest of the engine improvements that methanol makesfeasiblewould stillcontribute toan immediatelesseningof urban airpollution.

A. incorporating B. corporate C. operating D. cooperate

答案：1A 2C 3B 4D 5A 6D 7B 8A 9B 10A 11D 12B 13A

补充练习：

1. Althoughrecent years have seen substantial reductions in noxious pollutants fromindividual motor vehicles, the number of such vehicles .

A. have been steadily increasing B. hasbeen steadily increased

C. has been steadilyincreasing D. havebeen steadily increased

2. There isa growing realizationthat the only way to achieve further reductions in vehicleemissions is to replace conventional diesel fuel and gasoline withcleaner-burningfuels.

A. effective B. efficient C. sufficient D. supplement