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
[{'content': 'Commonest cause of pulmonary embolism is - \nSelect and explain. \nA. Thrombosis of leg veins, B. Thrombosis of prostatic veins, C. IVC thrombosis, D. Thrombosis of internal pudendal aery', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Thrombosis of leg veins Thrombi in deep vein of the leg accounts for more than 95% of cases of pulmonary embolism. The most common source of emboli are DVT of femoro-popliteal and iliac veins. But remember that : - Most common site of DVT is calf veins (Calf veins thrombosis are itself associated with a low risk for embolism, but when the thrombosis progresses proximally to involve the larger veins above knee, then the risk becomes very high.", 'role': 'assistant'}]