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: Pathology
Most common cause of pulmonary embolism? 
Select and explain. 
A. Thrombophlebitis, B. Endarteritis, C. Atheroscleroses, D. Lymphangitis
A: Thrombophlebitis
Answer: A: Thrombophlebitis 
Explanation: None