This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anaesthetic equipments, Subject name: Anaesthesia
Which of the following is low flow Oxygen delivery device 
Select and explain. 
A. Nasal cannula, B. Venti-mask, C. Bag & mask ventilation, D. Aerosol system
A: Nasal cannula
Answer: A: Nasal cannula 
Explanation: A nasal cannula is generally used wherever small amounts of supplemental oxygen is required, without rigid control of respiration, such as in oxygen therapy. Most cannulae can only provide oxygen at low flow rates--up to 5 litres per minute (L/min)--delivering an oxygen concentration of 28-44%. Rates above 5 L/min can result in discomfo to the patient.