PrepTest 159, Section 3, Question 19
When plants are growing quickly, they take more(67 more words not shown)
Which one of the following(8 more words not shown)
- AThe amount of(16 more words not shown)
- BIf the amount(28 more words not shown)
- CPlants in the(26 more words not shown)
- DIf the plants(21 more words not shown)
- EAny increase in(21 more words not shown)
Reading the argument
Plants don't always remove more carbon dioxide than they release. Whatever we might have expected before reading, these facts say that fast-growing plants do, while very slowly growing plants release more than they remove. What happens at an ordinary growth rate? We aren't told.
There's a possible cycle here: enough extra carbon dioxide raises tropical temperatures, and higher temperatures slow plant growth. Very slow growth could then mean more carbon dioxide released than absorbed. But watch the gaps before calling that an inevitable loop. A slowdown doesn't necessarily make growth very slow, and an extra release isn't necessarily a substantial increase in the total.
What we’re looking for
For a supported-inference question, keep those thresholds. I want a conclusion that follows the stated links without assuming every slowdown reaches the extreme or every extra bit of carbon dioxide is large enough to trigger the next effect.
Working the answers
- A
Nothing establishes an inevitable, accelerating increase. The passage gives relationships that operate under particular conditions; it doesn't tell us those conditions will keep being met, how fast the changes occur, or what other factors might affect releases. We can't turn a possible reinforcing process into an unavoidable forecast.
- B
A substantial increase in releases raises temperatures and slows plant growth in the tropics. But slower isn't necessarily very slow. Plants could go from growing very quickly to growing somewhat less quickly and still take out more carbon dioxide than they release. B needs the extra step from a relative slowdown to the very slow growth described in the passage.
- CCorrect
This explicitly gives us the needed starting condition: the tropical plants release enough carbon dioxide to increase total releases substantially. The passage says a substantial increase raises tropical temperatures, and higher tropical temperatures slow the plants' average growth. Those links establish C without assuming that every small release has the same effect.
- D
A slowdown alone doesn't establish very slow growth, a net release of carbon dioxide, or a substantial increase in total releases. And the passage doesn't say a resulting temperature increase must itself be substantial. D skips several steps and adds a claim about the size of the warming.
- E
We know that a substantial increase in carbon dioxide releases causes tropical warming. We aren't told it is the only possible cause of warming. Temperatures could rise for another reason, so an increase in temperature doesn't guarantee the substantial increase in releases that E requires.
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