Automobile manufacturers who began two decades ago to design passenger vehicles that were more fuel-efficient faced a dilemma in the fact that the lighter, more efficient vehicles were less safe on high-speed highways. However, the manufacturers avoided this dilemma by producing two types of passenger vehicles: a lighter vehicle for medium-speed, local transportation, and a heavier, safer vehicle for long-distance travel. Since most automobile traffic is local, a net savings in fuel use was achieved with no loss in safety.
Which one of the following, if true,
most seriously weakens the argument?
(A) Lighter vehicles can have smaller, more fuel-efficient engines without sacrificing power.
(B) Long-distance drivers are usually made on high-speed highways.
(C) Every automobile manufacturer now produces a greater number of fuel-efficient passenger vehicles than that manufacturer did two decades ago
(D) Many drivers use high-speed highways even when traveling locally
(E) Passenger vehicles today weigh less, on average, than did passenger vehicles two decades ago.
Source : LSAT
General Description: This question asks you to determine which response most weakens the argument. In approaching such questions, you should identify the conclusion of the argument, and find the response that, if true, undermines the argument's support for its conclusion.
A. Incorrect. If anything, this statement would tend to strengthen the argument, by eliminating a reason people might not actually use the lighter, more efficient cars.
B. Incorrect. This statement tends to strengthen the argument, by asserting that part of what the argument takes for granted (namely, that long-distance travel tends to take place on high-speed highways) is actually true.
C. Incorrect. The number of fuel-efficient cars being produced, and the distribution of such cars among the various automobile manufacturers, is irrelevant to the argument.
D. Correct. The argument is weakened to the extent that local travel takes place on high-speed highways. The argument says that "lighter, more efficient vehicles were less safe on high-speed highways." So if people use the more efficient but lighter, less-safe cars for local travel, and much local travel takes place on high-speed highways, the argument's conclusion that there is "no loss in safety" associated with the savings in fuel use is undermined.
E. Incorrect. The average passenger vehicle weight is irrelevant to the argument.
Difficulty Level: Easy
Tips and Pitfalls: It may seem obvious to say that if the question asks for weakening evidence, one should not choose strengthening evidence, and vice versa, but this is an easy mistake to make when answering questions quickly. If a statement does not strengthen an argument, do not assume that it must therefore weaken the argument.