According to the theory of constraints, a stockpile of work in process inventory should be stored A) as a buffer only in front of the constrained operation to keep it operating if there is a slowdown upstream. O B) as a buffer at all stages of the process to keep them operating in the event there is any disruption in the process. C C) nowhere. There should be no work in process inventories. O D) as a buffer after the constraint to keep downstream operations working in the event the constrained operation goes offline