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
What percentage of beta cell mass is destroyed when type 1 diabetes becomes evident? 
Select and explain. 
A. 20%, B. 40%, C. 60%, D. 80%
D: 80%
Answer: D: 80% 
Explanation: 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