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
Gastric motility is increased in: 
Select and explain. 
A. Acid in duodenum, B. Tryptophan in duodenum, C. Distension of stomach, D. Fatty food in stomach
A: Acid in duodenum
Answer: A: Acid in duodenum 
Explanation: Acid in duodenum