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': 'Dosage of benzyl penicillin in treatment of primary syphilis is : \nSelect and explain. \nA. 1.2 MU single i.m., B. 1.2 MU single i.v., C. 2.4 MU single i.m., D. 4.8 MU single i.m.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]