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
Pulmonary embolism is caused due to 
Select and explain. 
A. Deep vein thrombosis of leg, B. Increase in pulmonary tension, C. Fracture of pelvic region, D. Heart disease
A: Deep vein thrombosis of leg
Answer: A: Deep vein thrombosis of leg 
Explanation: None