This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: AIIMS 2017, Subject name: Anaesthesia
Highest concentration of oxygen is delivered through? 
Select and explain. 
A. Nasal cannula, B. Venturi mask, C. Bag and mask, D. Mask with reservoir
C: Bag and mask
Answer: C: Bag and mask 
Explanation: Bag and mask-100% O2 Venturi mask- 60% O2 Nasal cannula - 40% O2 Mask with reservoir- 80-90% O2