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
All of the following are risk factors for deep vein thrombosis (DVT) except - 
Select and explain. 
A. Duration of surgery more than thirty minutes, B. Obesity, C. Age less than forty years, D. Use of the oestrogen-progesterone contraceptive pills
C: Age less than forty years
Answer: C: Age less than forty years 
Explanation: None