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
Direct acting thrombin inhibitors are - 
Select and explain. 
A. Heparin, B. Hirudin, C. Warfarin, D. All
B: Hirudin
Answer: B: Hirudin 
Explanation: Ans. is 'b' i.e., Hirudin