An inventory system answers two important questions: when to order and how much to order. which of the following statements correctly explains how a q system (continuous review system) or a p system (periodic review system) answers these questions? a. under a q system, a fixed quantity is ordered every p time period. b. under a q system, an order is placed to replenish the inventory position up to the target level t when the inventory position reaches the reorder point r. c. under a p system, a fixed quantity is ordered when the inventory position reaches the reorder point r d. under a p system, an order is placed to replenish the inventory position up to the target level t every p time periods.