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': 'Metformin is NOT effective in lowering of blood sugar level in which of the following patients ? \nSelect and explain. \nA. Non diabetics, B. Obese diabetics, C. Type 2 diabetics, D. Diabetics not responding to sulfonylureas', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]