Gnpth
It is now known that to get the maximum out of a car engine one can do two things- use high octane fuel, which contains additives that extend the life and efficiency of the engine, or get the engine flushed at regular intervals, which removes all harmful substances from the engine. It has been shown by several studies that the use of high octane fuel is up to three times more effective in extending the life of the car engine than is the use of engine flushing. This does not, however, mean that engine flushing can play no role in extending the life of a car engine, because ______________________.
Which of the following logically completes the argument?
A) some studies have shown that using high octane fuel can lead to problems with a car's exhaust system.
B) high octane fuel costs much more than regular fuel and this cost is expected to increase even further over the next few years.
C) many car mechanics recommend the use of engine flushing over the use of high octane fuels.
D) the benefits of using high octane fuel are independent of the benefits of engine flushing.
E) Engine flushing when not done by expert mechanics, can cause permanent damage to the engine of the car.
Dear
Gnpth,
I'm happy to help with this.
First of all, here's a blog about complete-the-argument CR questions:
https://magoosh.com/gmat/2012/gmat-logic ... -argument/In the penultimate sentence, we are told of the benefits of high octane fuel, so it's clear that use of high octane fuel is recommended. Then the last sentence suggests that engine flushing is also recommended --- in other words, a responsible car-owner should do both. We need a reason why a responsible car-owner should do both, instead of just one or the other.
(A) some studies have shown that using high octane fuel can lead to problems with a car's exhaust system.A problem with high octane fuels --- this would cause us to re-think the penultimate sentence. It is not a reason to use both.
(B) high octane fuel costs much more than regular fuel and this cost is expected to increase even further over the next few years.
This would dissuade folks from using high octane fuels, but not necessarily for reasons related to what's best for the engine. This is irrelevant.
(C) many car mechanics recommend the use of engine flushing over the use of high octane fuels.First of all, mechanics recommend this presumably because they get paid for the service of flushing the engine, but they don't stand to gain if car-owners buy high octane fuels at the pump. More importantly, this contradicts the penultimate sentence, so it is not a good conclusion.
(D) the benefits of using high octane fuel are independent of the benefits of engine flushing.BINGO! If the benefits are independent, then that's an excellent reason to do both, because doing just one would provide none of the benefits of doing the other.
(E) Engine flushing when not done by expert mechanics, can cause permanent damage to the engine of the car.This may be, be no one is recommending not having it done by an expert. This is irrelevant.
Choice
(D) is the best answer here.
Mike