Final answer:
The correct data Cheryl would use is 'C. Best-selling product by day,' as it provides essential information for daily sales performance and production planning.
Step-by-step explanation:
Cheryl Steffan, as the operations manager for Nature's Bread Company, would need to analyze various pieces of data to determine the company's profitability and forecast production. The example that directly relates to her job would be C. Best-selling product by day. This data point provides insight into daily sales performance which is critical in understanding customer preferences, managing inventory, and preparing production schedules to meet the next day's demand efficiently. Data about customer identities, such as Craig Newmark is customer number 15467, or variables that might indirectly affect sales, such as changes in supply costs over the years or the performance impact of specific employees like Tony the baker, would not be as directly related to the daily sales numbers that are crucial for Cheryl's immediate operational decisions.