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: Pharmacology
[{'content': 'Direct acting thrombin inhibitors are - \nSelect and explain. \nA. Heparin, B. Hirudin, C. Warfarin, D. All', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Hirudin", 'role': 'assistant'}]