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
[{'content': 'What is the most common site of origin of thrombotic pulmonary emboli? \nSelect and explain. \nA. Deep leg veins, B. Lumen of left ventricle, C. Lumen of right ventricle, D. Mesenteric veins', 'role': 'user'}, {'content': 'Answer: A \nExplanation: An embolus is a detached intravascular mass that has been carried by the blood to a site other than where it was formed. Emboli basically can be thrombotic or embolic, but most originate from thrombi. These thromboemboli, most of which originate in the deep veins of the lower extremities, may embolize to the lungs.', 'role': 'assistant'}]