Final answer:
The appropriate control chart for tracking customer complaints at Millie's Fine Foods is a c-chart. It helps monitor the stability of complaints and identify any changes that require investigation and improvement.
Step-by-step explanation:
The appropriate control chart for tracking customer complaints at Millie's Fine Foods would be an c-chart, which is used for tracking the count of defects or nonconformities in a sample. For this chart, the number of customer complaints would be plotted over time, with control limits calculated based on the average number of complaints. By constructing this control chart, Millie's Fine Foods can monitor the stability of their customer complaints and identify any changes that may require investigation and improvement.