Self-study
Support Motor oil serves to lubricate engines and thus retard engine wear. █ █████ ███ █████████ ██ ██████ ███ █████████████ ██ ███████ ██████ ██ █████ ███ ██ █████ ████ ██ ████████ ████ █ ██████████ ████ ███████ ███ ███ ████ ███ ███████ ████ ██ █████████ ████ ██ ███████ ███ ██████████ ███ ████████ █████ ██ ███ ███████ ██████ ███████ ██████ ██ ███ ███ ███ ████ █████
Summarize Argument
The author concludes cheaper oil brands are "better buys" than more expensive oil brands. This is based on results showing that various brands of oil perform one basic function—retarding engine wear—with equal effectiveness.
Notable Assumptions
The author assumes that one brand of oil is better than another if it performs the same job at a lower price. But the only function of motor oil that was tested for was its ability to retard engine wear. The author must believe that motor oil doesn’t serve some other relevant purpose besides retarding engine wear. The author also assumes that different brands of oil will generally retard engine wear equally well, even in types of engines or vehicles not represented in the taxicab study.
5.
Which one of the following, ██ █████ ████ ███████ ███ █████████
a
Cheaper brands of █████ ███ ███ █████ ████ ██ █████████████ ██████████ █████████ ███ █████ ███ █████
If anything, this might slightly strengthen the argument. If knowledgeable mechanics are happy to use cheap motor oil, this seems to support the author’s argument that cheaper oils are better buys than more expensive ones.
b
Tests other than ██ ███ ███████ ██ ██████ ██████ ████ ████ ███ ████████ █████ ███ ███████ ██ █████ ████
Without knowing how those other tests judge cheap oils, we can’t draw any conclusions. We would need something to differentiate cheap oils from other oils.
c
The lubricating properties ██ ███ █████ ████ ███████████ ████ █████ ███ ███ ████ ██ █████████████ ██ ███████████ ██ █████
While it would be nice to know if cheaper oils deteriorate faster than more expensive ones, this choice just tells us that all oils deteriorate over time. On its own, this doesn't weaken the argument.
d
The engines of ████ ██████████ ████ ████ ████ ███ █████ ███ ███████ █████ █████ ██████ █████ ████ █ ███████ █████ ██ ████ ████ ██████ ██ ███████████████ ████ █████
We don’t know which brand of oil was used, and whether it was expensive or cheap. Even if we knew, this case of a few individual cars and one brand of oil is too specific to have much of an effect on the argument.
e
Ability to retard ██████ ████ ██ ███ ███ ████ ████████ ██ █████ ███ █████████ ██ ███ ███████ ██ ██ ███████
This tells us that there are other important factors in motor oil performance, which the author hasn't told us about. We therefore can’t say cheaper oils are “better buys” based only on their performance in slowing engine wear, without knowing how they perform other important functions.