Hey! I am having trouble understanding why A is incorrect. I do see how and why D works but I can't understand why A doesn't.
Here, we are given a correlation between the ad, price increase and drop in smoking. From the correlation, we get a causation that the ad is what caused the drop in smoking.
The flaw here is that the author overlooks all other alternate causes of the drop in smoking. In a strengthen question, an AC that denies an alternate causal explanation wins. For example, an AC that says or implies that X, an alternate cause for the drop in smoking, did not actually happen or that it can't be the cause will be the correct AC. And any AC that knocks out an alternate explanation for a given phenomenon automatically strengthens the proposed explanation.
Coming to AC A which says that the residents did not increase use of other forms of tobacco. Here, X i.e. the alternate cause, is given as people's increased use of other forms of tobacco. AC A denies this alternate cause.
The explanation that the 3% decrease in smoking happened because people switched over to other forms of tobacco seems like a valid alternate cause for the drop in number of smokers. (Cause: people switched to other forms of tobacco; effect: drop in smoking) It is such a small percentage and it is entirely reasonable that people switched how they wanted their tobacco kick. So, "3% people stopped smoking because they had switched over to other forms of tobacco instead" is a wonderful alternate causal explanation. Denying this alternate explanation increases the likelihood of ad causing the drop being true.
I get that D is better because it deals with the alternate explanation mentioned right there in the stimulus but how is A irrelevant?
TIA!