This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Anaesthesia
Which of the following systems can be used to produce PEEP? 
Select and explain. 
A. Spring system, B. Ball valve system, C. Pneumatic system, D. All the above
D: All the above
Answer: D: All the above 
Explanation: PEEP ValveA PEEP Valve is a device which maintains the airway at end exhalationSpring valve system is the simplest PEEP valve system. Other valve systems for PEEP are electronic, magnetic, pneumatic and ball valve.PEEP devices may be integrated into ventilator or may be separate devices that are attached directly into anesthesia circuit CPAP device or manual resuscitation bag.(Refer: stoelting's pharmacology and physiology in anaesthetic practice,5th edition, pg no.564,585)