This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vascular surgery, Subject name: Surgery
[{'content': 'The commonest cause of pulmonary embolism is \nSelect and explain. \nA. Thrombosis of prostatic veins, B. Thrombosis of leg veins, C. Inferior vena cava thrombosis, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Thrombi in a deep vein of the leg accounts for more than 95% of cases of pulmonary embolism. The most common source of emboli is DVT of femoropopliteal 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. Ref : Love & Bailey 24/e p866', 'role': 'assistant'}]