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: Pathology
Serotonin is mainly secreted by? 
Select and explain. 
A. Mast cells, B. Platelets, C. Neutrophills, D. Macrophages
B: Platelets
Answer: B: Platelets 
Explanation: o Serotonin (5-hydroxy tryptamine) is present in platelets and enterochromaffin cells.
o It is also present in mast cells of rodents, but not humans.