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: Physiology
[{'content': 'The extrinsic pathway of clotting is activated by \nSelect and explain. \nA. Release of tissue thromboplastin, B. Conversion of fibrinogen into fibrin, C. Formation of prothrombin, D. Release of calcium', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The extrinsic system is triggered by the release of tissue thromboplastin, a protein–phospholipid mixture that activates factor VII.', 'role': 'assistant'}]