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
Which of the following is involved in peristalsis by causing relaxation ? 
Select and explain. 
A. Substance P, B. Acetylcholine, C. VIP, D. Norepinephrine
C: VIP
Answer: C: VIP 
Explanation: Ans. is 'c' i.e., VIP In peristlasis :- Acetylcholine & substance P - Causing smooth muscle contraction. VIP, NO & ATP - Producing relaxation ahead of stimulus.