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 causes relaxation of bronchial smooth muscle? 
Select and explain. 
A. Leukotrienes, B. Vasoactive intestinal polypeptide, C. Acetylcholine, D. Cool air
B: Vasoactive intestinal polypeptide
Answer: B: Vasoactive intestinal polypeptide 
Explanation: None