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': 'The most important mechanism by which gram negative bacilli acquire chloramphenicol resistance is : \nSelect and explain. \nA. Decreased permeability into the bacterial cell, B. Acquisition of a plasmid encoded for chloramphenicol  acetyl transferase, C. Lowered affinity of the bacterial ribosome for chloramphenicol, D. Switching over from ribosomal to mitochondrial protein synthesis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]