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': "Risk factors of pulmonary embolism \nSelect and explain. \nA. 30 yrs female on OCP's, B. Pregnancy, C. Leg paralysis, D. All", 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'a' i.e. 30 yrs female on OCP's, 'b' i.e. Pregnancy, 'c' i.e. Leg paralysis", 'role': 'assistant'}]