A local consumer reporter wants to compare the average costs of grocery items purchased at three different supermarkets, A, B, and C. Prices (in dollars) were recorded for a sample of 60 randomly selected grocery items at each of the three supermarkets. In order to reduce item-to-item variation, the prices were recorded for each item on the same day at each supermarket.

Identify the dependent (response) variable for this experiment.

a) the supermarkets

b) the prices of the grocery items

c) the mean prices of the grocery items at each supermarket

d) the grocery items