This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
Cyanosis in trauma is interpreted as 
Select and explain. 
A. Early sign of hypoxia, B. Late sign of hypoxia, C. Absence of cyanosis means adequate tissue ventilation, D. Absence of cyanosis means adequate tissue oxygenation
B: Late sign of hypoxia
Answer: B: Late sign of hypoxia 
Explanation: Cyanosis is a bluish discoloration of the skin, mucous membranes, tongue, lips, or nail beds and is due to an increased concentration of reduced hemoglobin (Hb) in the circulation. Clinically evident cyanosis typically occurs at an oxygen saturation of 85% or less. Mild cyanosis may be difficult to detect Ref: guyton and hall textbook of medical physiology 12 edition