17.       
　　This ad recommends non-prescription Acid-Ease over non-prescription Pepticaid for relief of excess stomach acid. The only reason offered is that doctors have written 76 million more prescriptions for the full-strength prescription form of Acid-Ease than for full-strength Pepticaid. While this reason is relevant, and provides some grounds for preferring Acid-Ease over Pepticaid, it is insufficient as it stands because it depends on three unwarranted assumptions.

      The first assumption is that the prescription form of Acid-Ease is more popular among doctors. But this might not be the case, even though doctors have written 76 million more prescriptions for Acid-Ease. Acid-Ease may have been available for several more years than Pepticaid; and in the years when both products were available, Pepticaid might have actually been prescribed more often than Acid-Ease.来源：考试大

      The second assumption is that doctors prefer the prescription form of Acid-Ease for the reason that it is in fact more effective at relieving excess stomach acid. However, doctors may have preferred Acid-Ease for reasons other than its effectiveness. Perhaps Acid-Ease is produced by a larger, more familiar drug company or by one that distributes more free samples. For that matter, the medical community may have simply been mistaken in thinking that Acid-Ease was more effective. In short, the number of prescriptions by itself is not conclusive as to whether one product is actually better than another.来源：考试大

      The third assumption is that the milder non-prescription forms of Acid-Ease and Pepticaid will be analogous to the full-strength prescription forms of each. But this might not be the case. Suppose for the moment that the greater effectiveness of prescription Acid-Ease has been established; even so, the non-prescription form might not measure up to non-prescription Pepticaid. This fact must be established independently.来源：考试大

      In conclusion, this ad does not provide enough support for its recommending non-prescription Acid-Ease over nonprescription Pepticaid. To strengthen its argument, the promoter of Acid-Ease would have to show that (1) the comparison between the number of prescriptions is based on the same time period; (2) its effectiveness is the main reason more doctors have prescribed it, and (3) the comparative effectiveness of the two non-prescription forms is analogous to that of the prescription forms.