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
Guanylin is secreted by : 
Select and explain. 
A. C-cells., B. Paneth cells., C. Neurohypophysis., D. All of the above.
B: Paneth cells.
Answer: B: Paneth cells. 
Explanation: Paneth cells are endocrine cells located in crypts of lieberkuhn.