This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic histology, Subject name: Anatomy
Argentaffin cells in the GIT produce 
Select and explain. 
A. Gastrin, B. Pepsin, C. HCl, D. None of the above
D: None of the above
Answer: D: None of the above 
Explanation: Their granules contain a chemical called serotonin, which stimulates smooth muscle contractions.