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
Concentration of methemoglobin to appears cyanosis 
Select and explain. 
A. 5 gm/ dl, B. 2 gm/di, C. 1.5 gm/ dl, D. 12 gm/dl
C: 1.5 gm/ dl
Answer: C: 1.5 gm/ dl 
Explanation: C i.e. 1.5 01