LR Drill Set 1, Question 8
Carbon dioxide and water vapor in Earth's atmosphere(64 more words not shown)
Which one of the following(8 more words not shown)
- ASubstantially higher concentrations(29 more words not shown)
- BAny reduction in(35 more words not shown)
- CSubstantially higher concentrations(16 more words not shown)
- DA higher concentration(34 more words not shown)
- ESlightly higher concentrations(22 more words not shown)
Reading the argument
More heat stays in, but less heat gets in. Those are two different effects.
The gases reduce the heat that escapes after sunlight reaches Earth's surface. Increasing the concentrations substantially would strengthen that heat-retaining effect at least a little. But the passage adds another consequence: more cloud cover, which would significantly reduce the heat arriving from the sun in the first place.
Imagine watching two flows, incoming heat and outgoing heat. The clouds cut the incoming flow. The enhanced heat-retaining effect cuts the outgoing flow. Knowing the direction of both changes doesn't tell us which matters more to the final temperature. We would need enough information about their sizes to decide that.
What we’re looking for
For a supported inference, I would expect something that keeps those two effects separate. Higher concentrations can reduce heat coming in while also reducing heat escaping. An answer doesn't have to settle the overall temperature or summarize every sentence to be supported.
Working the answers
- ACorrect
The passage says substantially higher concentrations would enhance the effect that reduces heat radiating back into space. A states that consequence directly. It doesn't mention the added cloud cover, but a supported answer doesn't have to include every fact. This is one result we are given, even though the net temperature change remains unresolved.
- B
“Any reduction” reaches beyond the particular cause described. The passage connects these two effects to substantially higher concentrations of carbon dioxide and water vapor. It doesn't say that every possible way to reduce escaping heat also reduces incoming heat. B turns one described mechanism into a rule about all mechanisms.
- C
We don't know that the surface would cool. Reduced incoming heat pushes toward cooling, while reduced escaping heat pushes toward warming. The passage doesn't tell us enough to compare the total effects. “At least slightly” describes a minimum enhancement of heat retention, not a maximum that lets us conclude the cloud effect wins.
- D
The passage describes what happens with higher concentrations of both gases. That doesn't establish that extra water vapor is required for any increase in carbon dioxide to reduce incoming heat. We are given a situation that produces an effect, not a rule excluding every other situation. “Only if” adds that unsupported requirement.
- E
We are told about substantially higher concentrations, not slightly higher concentrations. We also lack a conclusion about the overall temperature effect even in the substantial-increase case. E makes both changes at once: it switches the size of the increase and declares a net result that the passage doesn't establish.
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