PrepTest 156, Section 4, Question 20
Azalea bushes flourish in acidic soil.(31 more words not shown)
Which one of the following(8 more words not shown)
- AMixing an acidic(12 more words not shown)
- BClay soil that(12 more words not shown)
- CWhenever clay soil(11 more words not shown)
- DSome plants do(5 more words not shown)
- EAzalea bushes do(11 more words not shown)
Reading the argument
Acidic soil works for azaleas. That doesn't mean it is the only soil that works, or that every other kind of plant dislikes it. We know only what happens to these bushes in this kind of soil. Now we're told that clay, though rarely acidic on its own, can be mixed with other soils to make an acidic mixture. That gives us a way to create conditions in which azaleas flourish.
What we’re looking for
But notice the shift from that mixture to the conclusion about clay soil. We needed to mix something into the clay to get the result described. I want to be careful about what the argument is calling clay at that point. The conclusion doesn't say 'pure clay,' so we shouldn't add that restriction ourselves. For the required-assumption question, I don't yet have a precise answer in mind; I want to see what must connect the soil we make with the soil named in the conclusion.
Working the answers
- A
'Always' is much stronger than the argument needs. Mixing an acidic soil with just any other soil doesn't have to preserve acidity every time. The argument needs a suitable mixture to be possible, not a guarantee about every mixture involving an acidic soil.
- BCorrect
Here is the missing connection: the resulting mixture must still count as clay soil. Otherwise, we would have shown that azaleas can flourish in a different type of soil produced using clay, not that they can flourish in clay soil. The argument depends on retaining that description after at least some of the relevant mixing.
- C
Again, possibility isn't a universal guarantee. The passage says clay can be mixed with other soils to create an acidic soil. It doesn't require every combination of clay and another soil to turn out acidic. One suitable kind of mixture would be enough for the argument's proposed route to work.
- D
Other plants aren't part of this reasoning. All plants could flourish in acidic soil, or some could fail to do so, without changing the connection needed for this conclusion about azaleas. We shouldn't infer facts about other species from the one favorable condition described for these bushes.
- E
Flourishing in the treated soil doesn't require doing exactly as well as in naturally acidic soil. Azaleas could flourish in both while doing even better in one. The argument needs success in soil that still counts as clay, not a comparison establishing equal performance between the two kinds of acidic soil.
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