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: Biochemistry
Which vitamin is associated with glycogen phosphorylase? 
Select and explain. 
A. Pyridoxin, B. Niacin, C. Riboflavin, D. Thiamine
A: Pyridoxin
Answer: A: Pyridoxin 
Explanation: Pyridoxin Pyridoxal phosphate is an essential cofactor for glycogen phosphorylase