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': 'Conversion of prothrombin to thrombin requires: \nSelect and explain. \nA. V only, B. V and Ca++, C. XII, D. X and Ca++', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]