PrepTest 128, Section 2, Question 13
Scientist: There is little doubt that the ice(54 more words not shown)
Which one of the following(10 more words not shown)
- AExcessive growth of(18 more words not shown)
- BIf the carbon(15 more words not shown)
- CAn excessive growth(12 more words not shown)
- DIf unusually rich(19 more words not shown)
- EUnusually rich growth(12 more words not shown)
Reading the argument
Plants caused the ice ages? That is a striking claim. How would it work? Perhaps heavy vegetation removes so much carbon dioxide that the atmosphere retains less heat and the planet cools.
That is the mechanism the scientist supplies. Vegetation converts carbon dioxide into oxygen; carbon dioxide helps retain the sun's heat; and depleting it can cool Earth enough to bring about an ice age. Think of losing some of the atmosphere's heat-retaining capacity.
I can follow that proposed mechanism while still wondering what evidence shows it actually caused the ice ages. Showing how something could happen isn't necessarily showing that it did happen.
What we’re looking for
But the task is to identify the scientist's main conclusion, not decide whether it has been proved. The opening sentence makes the central claim: unusually rich vegetation almost certainly caused the ice ages. The remaining sentences explain how that proposed cause would work. That's the claim our answer needs to restate.
Working the answers
- A
'Could have caused' is weaker than the scientist's conclusion. The scientist says there is little doubt that vegetation did cause the ice ages. A restates the possibility of the mechanism working while leaving out the confidence in what actually happened.
- B
This is a step in the explanation: depleting carbon dioxide produces cooling and an ice age. Even though the passage introduces it with 'Thus,' it supports the larger claim about what caused the ice ages. The main conclusion is about vegetation's actual role, not just what would happen if carbon dioxide were depleted.
- C
This supplies an earlier link in the mechanism, from vegetation to reduced carbon dioxide. The scientist uses that link to explain how vegetation could cause an ice age. It is supporting material, not the ultimate causal conclusion.
- D
This says what the mechanism must have been if vegetation caused the ice ages. It doesn't assert that vegetation actually was the cause. The scientist makes that causal claim directly and confidently, so the conditional statement doesn't capture the main point.
- ECorrect
'Almost certainly' captures 'there is little doubt,' and the rest identifies the same cause and result: unusually rich vegetation worldwide caused the ice ages. This is the opening claim that the chain of reasoning is intended to support.
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