The caffeine in coffee stimulates the production of irritating acid in the stomach. But darker roasts of coffee, produced by roasting the coffee beans longer, contain more N-methylpyridinium (NMP) than lighter roasts, and NMP tends to suppress production of acid in the stomach. Ttherefore if you drink caffeinated coffee, darker roasts will irritate your stomach less than lighter roasts. The answer to which one of the following questions most helps in evaluating the argument? ['Does a reduction in acid production in the stomach have an adverse effect on stomach function?', 'Does extending the roasting time of coffee beans increase the amount of caffeine present in the brewed coffee?', 'Would coffee drinkers who drink caffeinated coffee increase their coffee consumption if the coffee they drank contained less caffeine?', 'Do lighter roasts of coffee have any important health benefits that darker roasts of coffee lack?']