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
Buerger's angle that indicates severe ischaemia is 
Select and explain. 
A. 120°, B. 80°, C. 60°, D. 30°
D: 30°
Answer: D: 30° 
Explanation: If Buerger's angle is < 30°, it indicates severe ischaemia.