A positive correlation has been found between the amount of soot in the atmosphere of cities and the frequency of a certain ailment among those cities' populations. However, Conclusion the soot itself probably does not cause this ailment, since Support in cities where there are large amounts of soot in the air, there are usually also high concentrations of many other air pollutants.
The author's conclusion is the claim that soot in cities' atmospheres likely doesn’t cause a certain ailment that is positively correlated with atmospheric soot concentration. The premise for this conclusion is that cities with lots of soot in the air usually also have lots of other pollutants in the air. We aren't given any details on whether these other pollutants cause this ailment.
The author assumes that the ailment in question is probably caused by at least one of the other pollutants, and not by soot. In other words, without specific evidence against soot or for any other pollutant, the author assumes that the positive correlation between the amount of soot in the atmosphere and the frequency of this ailment is not the result of causation.
Which one of the following statements, if true, most weakens the argument?
In cities where there are high concentrations of many air pollutants but little if any soot in the air, the frequency of the ailment is just as high, on average, as it is in cities where there are large amounts of soot in the air.
This strengthens the author’s argument. Since the ailment also occurs in places where there’s little to no soot in the air, it seems more likely that other pollutants, not soot, are causing the ailment.
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).
If the ailment rarely occurs except in cities in which there are large amounts of soot in the air, then the soot is probably the cause of the ailment.
It definitely seems true that if the ailment mainly showed up only in cities with high levels of soot in the air, then soot would be the likely cause. But We don't know if the \"if\" part of this statement ever occurs. Since this is a hypothetical statement, it can’t weaken the argument.
In each of the cities where there are large amounts of soot in the air but little other air pollution, the frequency of the ailment is at least as high as it is anywhere else.
This weakens the author's argument. The ailment is just as common when there is only soot in the air, and not many other pollutants. This makes soot seem like the likely cause of the ailment, contrary to the author's conclusion.
Weaken: Introduce or suggest an alternate explanation for the target phenomenon.
Strengthen: Helps to eliminate an alternate explanation for the target phenomenon.
If high concentrations of many different pollutants in a city's air are correlated with a high frequency of the ailment among that city's population, then it is possible that two or more of those pollutants each causally contributes to the ailment.
Notice that, while this answer choice leaves open the possibility that soot is a contributing factor to the ailment, it also leaves open the possibility that it's several of the other pollutants, but not the soot, that cause the ailment. So on its own, this answer choice doesn't give us a reason either to favor or discard the author's conclusion. It doesn't make soot more or less likely to be a cause of the ailment. So this doesn't weaken the conclusion.
In cities in which there are high concentrations of many air pollutants, there are generally also high concentrations of other forms of pollution that are very likely to contribute causally to the ailment.
While this answer choice technically leaves open the possibility that soot causes the ailment, it could work just as well as a neutral description of the city atmospheres described by the author in the stimulus. This answer choice on its own doesn't make soot more or less likely to be the cause of the ailment, so it doesn't weaken the conclusion.
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).
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