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': 'Which of the following is the longest acting oral anticoagulant ? \nSelect and explain. \nA. Bishydroxycoumarin, B. Warfarin, C. Acenocoumarol, D. Phenindione', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Bishydroxycoumarin Bishydroxycoumarin (Dicumarol) is the longest acting oral anticoagulant. Ethylbiscoumacetate is the shoest acting anticoagulant.", 'role': 'assistant'}]