This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
[{'content': 'What percentage of beta cell mass is destroyed when type 1 diabetes becomes evident? \nSelect and explain. \nA. 20%, B. 40%, C. 60%, D. 80%', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Features of diabetes do not become evident until a majority of beta cells are destroyed (70-80%). At this point, residual functional beta cells exist but are insufficient in number to maintain glucose tolerance.Ref: Harrison 19e pg: 2403', 'role': 'assistant'}]