Which of these conditions is NOT necessary for the economic order quantity model to be valid? Select one: a. The item has a constant safety stock b. The item has a constant lead time c. The item has a constant price d. The item has a constant demand. If a decrease in unit price causes the average demand rate to increase, which one of these would not increase? Select one: O a. the EOQ b. lead time c. annual holding cost d. safety stock