This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Varicose Veins, Subject name: Surgery
[{'content': 'Primary cause of varicose veins - \nSelect and explain. \nA. Incompetent valve perforators, B. Intrinsic abnormality of venous wall, C. Venous hypertension, D. Decrease in collagen in venous wall', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is A.', 'role': 'assistant'}]