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 statements is not true for heparin \nSelect and explain. \nA. Acts by activating anti-thrombin III, B. Protamine sulphate antagonizes its action, C. Requires aPTT monitoring in patient, D. Has only in vivo anticoagulant action', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]