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: Physiology
Glucagon is secreted by: 
Select and explain. 
A. Alpha cells of pancreas, B. Beta cells of pancreas, C. Gamma cells of pancreas, D. None of the above
A: Alpha cells of pancreas
Answer: A: Alpha cells of pancreas 
Explanation: None