Thanks for the question! This is certainly a tricky question. But negating (A) just says that “urban pollution has doubled in the past decade.” So what? We already showed in the argument that pollution wasn’t the cause. Because we showed that when there’s no pollution (and thus no cause), there’s still increased death rates from asthma (and so the effect is still there). If you take away the purported cause and the effect remains, then it’s not really the cause. So urban pollution is irrelevant and so the argument doesn’t depend on this assumption.
Hope this helps! Feel free to ask any other questions that you might have.
