The question says, "Each of the following, if true, provides support to the argument EXCEPT:"
We're looking for an answer choice that does not strengthen the argument. The correct choice will either be irrelevant or will weaken the argument.
(B) says, "Records of asthma deaths are as accurate for the past twenty years as for the past ten years."
(B) actually strengthens this argument because it rules out an alternative cause (bad medical records). Based on (B) asthma death rate reporting hasn't become more accurate within the last 20 years, and this really hurts the alternative explanation about more accurate reporting being the reason there's such a higher number of death rates for asthma now, so it strengthens the author's position. Thus, we can get rid of this choice.
(A) says, "Urban populations have doubled in the past decade."
(A) is great because it's totally irrelevant to the argument. It's the rate of asthma sufferers that has increased, and rates are percentages. Absolute numbers, such as urban populations doubling (what (A) says), are totally irrelevant when we're looking at rates/percentages, so (A) is the winner, as it doesn't strengthen the argument.
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