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
Antegrade peristalsis due to? 
Select and explain. 
A. Ach, B. Serotonin, C. Substance P, D. VIP
A: Ach
Answer: A: Ach 
Explanation: - Excitatory neurotransmitters in ENS are Acetylcholine & substance P - Inhibitory neurotransmitters in enteric nervous system are NO & VIP - Acetylcholine is main excitatory neurotransmitter responsible for antegrade peristalsis