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 is/are the GI hormones stimulating insulin secretion? 
Select and explain. 
A. GIP, B. Gastrin, C. Secretin, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: GIP, Gastrin, Secretin & CCK. Stimulating factor for insulin secretion: Glucose - Relationship between glucose concentration & insulin secretion is "SIGMOIDAL" Mannose Amino acids (arginine, leucine) Intestinal hormones -GLP -1. GIP. Gastrin. Secretin. CCK b-keto acids Parasympathetic stimulation - Acetylcholine cAMP b-adrenergic stimulation. Drugs:Endocrine hormones like Growth hormone, Glucagon & Glucocoicoids. Theophylline. Sulfonylureas