A Local Consumer Reporter Wants to Compare the Average Costs

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. $$\begin{array} { c l r c c } \hline & { \text { Item } } & \mathrm { A } & \mathrm { B } & \mathrm { C } \\\hline \text { 1) } & \text { paper towels } & 1.21 & 1.41 & 1.36 \\\text { 2) } & \text { cereal } & 2.81 & 3.26 & 3.01 \\\text { 3) } & \text { floor cleaner } & 6.03 & 5.91 & 6.92 \\\text { | } & \text { | } &\text { | } &\text { | } &\text { | } \\\text { 59) } & \text { shaving cream } & 1.09 & 0.99 & 1.05 \\\text { 60) } & \text { canned green beans } & 0.45 & 0.60 & 0.37 \\\hline\end{array}$$ Identify the blocks for this experiment.

A) the 60 grocery items
B) the three supermarkets
C) the 60 × 3 = 180 prices
D) the day on which the data were collected