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
Risk factors of pulmonary embolism 
Select and explain. 
A. 30 yrs female on OCP's, B. Pregnancy, C. Leg paralysis, D. All
D: All
Answer: D: All 
Explanation: Ans. is 'a' i.e. 30 yrs female on OCP's, 'b' i.e. Pregnancy, 'c' i.e. Leg paralysis