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: Biochemistry
[{'content': 'True among all is \nSelect and explain. \nA. Repressor is dimer and a positive regulator, B. CRP is gratuitous inducer, C. Lactose is positive regulator, D. Catabolite repression is mediated by CRP', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Catabolite repression is mediated by CRP', 'role': 'assistant'}]