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?

Question $1$Select one:

A$.$

Under a P system, a fixed quantity Q is ordered when the inventory position reaches the reorder point R$.$

B$.$

Under a Q system, a fixed quantity is ordered every P time period.

C$.$

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$.$

D$.$

Under a P system, an order is placed to replenish the inventory position up to the target level T every P time periods.