To boost pastry sales, the cafe began playing soft jazz during weekend mornings. Over the last two weekends, pastry revenue rose 20 percent, and neither menu nor staffing changed during that period. Regulars have not complained about the new music. Therefore, the music must have caused the bump, so we should keep the jazz every weekend. We tried nothing else to attract customers.
Which one of the following, if true, most seriously weakens the argument?
- Studies show background music can increase dwell time in cafes.
- A weekend-only coupon for discounted pastries was mailed to neighborhood residents just before the increase. (correct answer)
- Some customers prefer silence when they read.
- The pastry recipes and prices were unchanged during the period.
- The volume of the jazz was kept low to avoid disturbing conversations.
Explanation: The argument assumes the music caused the sales bump; a targeted pastry coupon provides a more direct alternative explanation. The other options either support the music effect or are irrelevant to the causal claim.