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: Surgery
According to American society of Anaesthelogists the physical status of a patient with severe incapacitating systemic disease that is a constant threat to life may be classified as: 
Select and explain. 
A. ASA 1, B. ASA 2, C. ASA 3, D. ASA 4
D: ASA 4
Answer: D: ASA 4 
Explanation: None