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
[{'content': 'Which of the following coagulation factors is deficient in\nclassical haemophilia: \nSelect and explain. \nA. VIII, B. IX, C. X, D. XII', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]