PrepTest 108, Section 2, Question 5
Smith's new grazing land consists entirely of fescue(61 more words not shown)
Which one of the following(7 more words not shown)
- AAt least one(20 more words not shown)
- BAt least some(18 more words not shown)
- CThe fungus that(15 more words not shown)
- DThe cows are(20 more words not shown)
- EThe fungus that(14 more words not shown)
Reading the argument
Can the cows actually detect the fungus? Knowing to avoid something that made you ill isn't helpful if you can't tell where it is.
Half the grass contains the harmful fungus. The author expects the cows to learn to eat only the other half because cows avoid a patch when they sense something in it that previously made them ill. That last condition does a lot of work: if they sense it. Imagine a cow becoming ill after grazing but finding every patch indistinguishable the next day. The tendency to avoid a detected substance wouldn't tell that cow which patch to choose.
What we’re looking for
The necessary-assumption question asks what the author needs for this proposed learning to work. I'd look for the ability to sense this particular fungus. We don't need to decide whether the farmer should replace the grass or change how the field is managed. The argument predicts what the cows themselves will learn to do.
Working the answers
- A
A different fungus in the other grass doesn't establish whether cows can identify and avoid the fungus that made them ill. The harmful fungus could be the only species present, or other species could coexist with it. Neither situation is required by the proposed explanation of the cows' behavior.
- BCorrect
At least some cows made ill by this fungus can sense it in the grass. The argument needs that ability somewhere for its stated avoidance mechanism to work. If none of the affected cows could detect the fungus, the fact that cows avoid harmful substances they sense would give us no basis for predicting this behavior.
Notice the limited wording: 'at least some.' This doesn't prove that every one of Smith's cows will successfully graze on safe grass. A necessary assumption needn't establish the whole conclusion by itself. B supplies an ability the reasoning cannot do without.
- C
The fungus could also grow in another variety of grass. That wouldn't stop these cows from sensing and avoiding it here. The argument concerns their behavior on Smith's land, not whether fescue is the fungus's only possible host.
- D
Sheep or some other grazing animals might also become ill from this fungus. The cows could still learn to avoid it. Nothing about the cows' predicted behavior requires them to be the only animals affected.
- E
Whether the fungus can be removed without destroying the grass concerns a possible way for the farmer to manage the field. The argument instead relies on the cows learning to choose grass without the fungus. That explanation could work whether removal is easy, difficult, or impossible.
More Necessary Assumption questions
Learn the LSAT our way
Our platform drills Necessary Assumption questions at your level and adjusts as you improve.