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: Medicine
The most common source of pulmonary embolism 
Select and explain. 
A. Amniotic fluid embolism, B. Renal artery embolism, C. Large veins of leg, D. Cardio thoracic surgery
C: Large veins of leg
Answer: C: Large veins of leg 
Explanation: None