This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Local and Regional Anesthesia, Subject name: Anaesthesia
What is this instrument used for: 
Select and explain. 
A. Ventilation, B. Feeding, C. TURP, D. Cholestomy
A: Ventilation
Answer: A: Ventilation 
Explanation: Ans. (a) VentilationRef.: Miller's Anaesthesia 7th ed. / 2139* AMBU Bag stands for Ambulatory Breathing Unit.* It is a self-refilling bag-valve-mask unit with 1-1.5L capacity, used for ventilating and oxygenating intubated patients, allowing both spontaneous and artificial respiration.