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: Medicine
Minimum concentration of reduced hemoglobin required for cyanosis is - 
Select and explain. 
A. 1 gm/dl, B. 3gm/dl, C. 7gm/dl, D. 9gm/dl
C: 7gm/dl
Answer: C: 7gm/dl 
Explanation: None