GMAT逻辑题目:

　　【逻辑】

　　Thefaster a car is traveling, the less time the driver has to avoid a potentialaccident, and if a car does crash, higher speeds increase the risk of afatality. Between 1995 and 2000, average highway speeds increased significantlyin the United States, yet, over that time, there was a drop in the number ofcar-crash fatalities per highway mile driven by cars.

　　Whichof the following, if true about the United States between 1995 and 2000, mosthelps to explain why the fatality rate decreased in spite of the increase inaverage highway speeds? A. The average number ofpassengers per car on highways increased.

　　B. There were increases in boththe proportion of people who wore seat belts and the proportion of cars thatwere equipped with airbags as safety devices.

　　C. The increase in average highwayspeeds occurred as legal speed limits were raised on one highway after another.

　　D. The average mileage driven onhighways per car increased.

　　E. In most locations on thehighways, the density of vehicles on the highway did not decrease, althoughindividual vehicles, on average, made their trips more quickly.

GMAT逻辑答案:

　　Reasoning

　　What could explain why the number of fatalities per highway mile driven declined even as average highway speeds increased? We are told that higher speeds mean a higher risk of fatalities, other things being equal. Consequently, the increasing highway speeds between 1995 and 2000 should have led to more fatalities per highway mile driven. Since the fatalities per mile driven actually decreased, some countervailing factor must have increased driving safety more than enough to compensate for the danger of the higher speeds. Thus, find an answer option suggesting how a factor that increased driving safety became more common or effective between 1995 and 2000.

　　A. More passengers per car would likely mean even more fatalities per highway mile driven, since more people would die per car accident.

　　B. Correct. More seatbelts and airbags would have probably reduced the average number of fatalities per car accident, resulting in fewer fatalities per mile driven even if the higher speeds resulted in more car accidents.

　　C. This cannot help explain the decrease in fatalities. Driving at a higher speed probably increases the risk of a fatal car accident regardless of whether the speed is legal or illegal.

　　D. Fewer accidents per highway mile driven could explain why the average highway mileage per car increased (since some cars would have gone more miles before crashing), but the converse is not correct: the increased average mileage could not explain why there were fewer accidents per mile driven.

　　E. Instead of explaining why there was a decrease in the number of fatalities per highway mile driven, this merely rules out the possibility that the explanation was a lower density of cars on the highways.

　　The correct answer is B.

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