A mass provider of copy services wants to assess the stability of their service process. To collect performance data, they use a survey, asking customers to rate their services across 5 different characteristics (where each service characteristic is either acceptable or a concern). Thus, each customer may have 0, 1, 2, 3, 4, or 5 concerns. Currently, they have 3 main customer accounts and numerous other small accounts. Each week, they obtain 30-50 customer surveys. Which of the following would you MOST LIKELY recommend to assess the stability of their service process over the past 20 weeks? Group of answer choices a. Monitor number of concerns per customer per week using a U-Chart b. Monitor the number of customers with 3 or more concerns using an X-bar Charts c. Monitor % of customers with 4 or more concerns per day using a P-Chart d. Monitor average concerns per week using a U-chart