Summarize Argument: Causal Explanation
The scientist confidently claims that the ice ages were caused by widespread, unusually rich growth of vegetation. His reasoning is that vegetation converts oxygen into CO2. CO2 retains heat. Excess vegetation caused a reduction in CO2, causing the earth to cool due to a lack of heat retention. This cooling caused the ice ages.
Identify Conclusion
The conclusion is the scientist’s explanation for the ice ages: “There is little doubt that the ice ages were caused by the unusually rich growth of vegetation worldwide.”
A
Excessive growth of vegetation worldwide could have caused one or more ice ages by depleting the carbon dioxide in the atmosphere.
This is too weak to match the conclusion. The scientist claims that the excessive growth of vegetation almost definitely caused all of the ice ages.
B
If the carbon dioxide in the atmosphere is depleted, the earth cools significantly, thereby causing an ice age.
This is part of the causal explanation that shows how excessive vegetation would cause an ice age.
C
An excessive growth of vegetation causes the carbon dioxide in the atmosphere to be depleted.
This is also part of the chained explanation showing the process of how excessive vegetation would cause an ice age.
D
If unusually rich growth of vegetation caused the ice ages, it undoubtedly did so by depleting the carbon dioxide in the atmosphere.
This “if” statement does not match the conclusion. The author definitively states that the phenomenon did happen, and it happened by this process.
E
Unusually rich growth of vegetation worldwide was almost certainly the cause of the ice ages.
This accurately matches the strength and content of the conclusion. “Almost certainly” matches the author’s “there is little doubt” that this unusual vegetation growth caused the ice ages.
Summarize Argument: Phenomenon-Hypothesis
The author concludes that exercise can increase life span. This is because the subjects in a study who exercised were less likely to die during the study than the subjects who didn’t exercise.
Notable Assumptions
The author assumes that there was no prior correlation between people who exercised and were in good health, or people who didn’t exercise and were in poor health. If people on the verge of dying didn’t exercise given their health condition, then the study wouldn’t indicate anything about the effects of exercise.
A
The subjects who did not exercise regularly during the study tended to have diets that were more unhealthy.
This weakens the author’s argument by bringing in a third factor: diet. Perhaps the people who didn’t die were saved by their diets rather than by exercise.
B
The subjects who did not exercise regularly during the study tended to blame their lack of exercise on a lack of time.
This doesn’t do much. Perhaps those people had little time because they were stressed about other things, and the stress ended up damaging their health.
C
A large number of the deaths recorded were attributable to preexisting conditions or illnesses.
This severely damages the author’s argument. People died because of their preexisting conditions rather than their lack of exercise.
D
Whether or not a given subject was to exercise during the study was determined by the researchers on a random basis.
There was no connection between prior health and exercise. This defends against the obvious weakener that only already-healthy people were exercising.
E
A person who exercises regularly is probably doing so out of concern for his or her own health.
We don’t care what motivated the participants to exercise.