This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
The concentration of methemoglobin to cause cyanosis- 
Select and explain. 
A. 5 gm/dl, B. 2 gm/dl, C. 1.5 gm/dl, D. 12 gm/dl
C: 1.5 gm/dl
Answer: C: 1.5 gm/dl 
Explanation: For Cyanosis to occur,
Sulfhemoglobin should be equal or more than 0.5gm/dL
Methemoglobin should be equal or more than 1.5gm/dL
Deoxygenated hemoglobin should be equal or more than 5gm/dL