This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pulmonary Embolism, Subject name: Medicine
The most common source of pulmonary embolism is : 
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: Ans. is 'c' large veins of leg (Ref Harrison, 17/e, p 1651 & 16/e, p 1561 (15/e, p. 1509)).Remember thatMC site for deep vein thrombosis - Calf vein*.But MC source for pulmonary emboli - Proximal vein of lower extremity (femoral vein*).