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: Medicine
Enzyme deficient in diabetes mellitus is: 
Select and explain. 
A. Glucokinase, B. Hexokinase, C. Phosphorylase, D. Pyrophosphate dehydrogenase
A: Glucokinase
Answer: A: Glucokinase 
Explanation: None