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': 'Chloramphenicol act through action on : \nSelect and explain. \nA. 50S ribosome, B. 30S ribosome, C. Nucleus, D. Mitochondria', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]