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': 'Anticoagulant not used in vitro is - \nSelect and explain. \nA. Heparin, B. Warfarin, C. Oxalate, D. Citrate', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Warfarin o Oral anticoagulants have only in vivo action (not in vitro). o Heparin is used both in vivo and in vitro. o Oxalate and citrate are used in vivo.", 'role': 'assistant'}]