This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal System, Subject name: Physiology
Duodenum and Jejunum secrete ALL EXCEPT 
Select and explain. 
A. CCK, B. Secretin, C. GIP, D. VIP
D: VIP
Answer: D: VIP 
Explanation: V.I.P. is a inhibitory neurotransmitter found in nerves in the gastrointestinal tract and thus is not itself a hormone.