Because of steep increases in the average price per box of cereal over the last 10 years, overall sales of cereal have recently begun to drop. In an attempt to improve sales, one major cereal manufacturer reduced the wholesale prices of its cereals by 20 percent. Since most other cereal manufacturers have announced that they will follow suit, it is likely that the level of overall sales of cereal will rise significantly. Which of the following would it be most useful to establish in evaluating the argument? ['Whether the variety of cereals available on the market has significantly increased over the last 10 years', 'Whether the high marketing expenses of the highly competitive cereal market led to the increase in cereal prices', 'Whether the prices that supermarkets charge for these cereals will reflect the lower prices the supermarkets will be paying the manufacturers', 'Whether the sales of certain types of cereal have declined disproportionately over the last 10 years']