PrepTest 151, Section 2, Question 18
In grasslands near the Namib Desert there are(39 more words not shown)
Which one of the following,(7 more words not shown)
- ADying grass plants(11 more words not shown)
- BThe grasses that(18 more words not shown)
- CThe soil in(16 more words not shown)
- DFairy circles tend(11 more words not shown)
- ESpecies of animals(12 more words not shown)
Reading the argument
Did the termites make the bare circle, or did they move in after something else made it?
Finding termites in every investigated circle gives us a connection. It doesn't yet tell us how the circle formed. Another animal might have removed the vegetation, or something in the soil might have killed it. The resulting bare patch could then be attractive to termites. Those are possibilities, not established explanations.
The hypothesis is more specific than just saying termites are present: their burrowing causes the vegetation-free circles.
What we’re looking for
To strengthen it, we could eliminate a competing explanation or learn how the termites' activity damages the plants. For example, evidence of a feeding or chemical mechanism could help connect their presence to the plants' death. Let's see what the choices actually supply.
Working the answers
- ACorrect
At first, the location of the damage may seem like a minor detail. Why should roots matter? Because the proposed cause is burrowing. The damage is underground, where that activity would affect the plants, and it appears in circles that are just forming.
That is a better fit with the proposed mechanism than simply finding termites in an already bare patch. It doesn't explicitly prove that termites damaged the roots, and other causes of root damage might remain. But we are strengthening a hypothesis, not proving it beyond every alternative. A connects the kind and location of damage to the particular activity the scientists suspect.
- B
This is tempting because drought is a possible competing explanation. If the dying plants could withstand the region's droughts, that would give us a reason to look elsewhere. But B concerns the grass around the circles, not necessarily the vegetation that died inside them.
We can't simply transfer the surrounding grass's drought resistance to everything that once grew in the bare area. B may offer indirect encouragement against a drought explanation, but it doesn't establish that drought couldn't affect the vegetation at issue. A gives the more direct connection between the proposed underground activity and the damage in newly forming circles.
- C
More water doesn't tell us what killed the plants or how termite burrowing caused their loss. We would need another connection between the water content and the proposed mechanism. Don't assume that more water must always help plants, or that this fact automatically weakens the hypothesis. Its relevance to the cause of these circles hasn't been established.
- D
Nearby circles could share any number of conditions. To turn this clustering into support for termites, we'd need information linking the locations to termite activity or the way colonies spread. D supplies neither. The bare patches being close together doesn't identify what created them.
- E
Animals that eat termites might be attracted to an area where termites live. But we already know the termites are present. The unanswered question is whether they created the circles or arrived afterward. Predators could find termites there under either explanation, so their presence doesn't supply the missing connection to the circles' origin.
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