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': 'Heparin inhibits Xa by \nSelect and explain. \nA. Blocking vitamin K mediated activation of Xa, B. Activating Antithrombin III, C. Direct breakdown of Xa, D. Blocking P2 Y12 receptor of ADP', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Heparin contains pentasaccharide unit that activates Antithrombin III & inhibits factor Xa (Thus it is a indirect thrombin inhibitor).\nUnfractionised heparin also contains a heteropolysaccharide unit that inhibits factor II a.\nLMWH lacks this heteropolysacchoride unit and therefore inhibitors factor Xa only.', 'role': 'assistant'}]