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
Longest acting Insulin among the following 
Select and explain. 
A. Insulin Glargine, B. Insulin Detemir, C. Insulin Degludec, D. NPH
C: Insulin Degludec
Answer: C: Insulin Degludec 
Explanation: insulin degludec which has duration of action upto 42hours Ref Harrison 20th edi page no 2863, tab 397-4