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
Brodie -Trendlenburg test demonstrates- 
Select and explain. 
A. Mid - thigh perforation, B. Deep vein thrombosis, C. Sapheno - femoral incompetence, D. Calf perforators
C: Sapheno - femoral incompetence
Answer: C: Sapheno - femoral incompetence 
Explanation: None