This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anesthesia Machine, Subject name: Anaesthesia
What is present day application of oxygen concentrators include:- 
Select and explain. 
A. Domicillary use, B. Supplying ambulance, C. Supplying anesthesia medicine, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Oxygen concentrators are widely used to provide oxygen-enriched gas for multiple use: i. Domicillary use ii. Remote locations iii. For oxygen pipeline supply iv. Anesthesia machine