This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Physiology
Which of the following is a Cholagogue? 
Select and explain. 
A. Secretin, B. Bicarbonate, C. CCK, D. Bile salts
C: CCK
Answer: C: CCK 
Explanation: Substances that cause gallbladder contraction are called cholagogues. A well-known cholagogue is a cholecystokinin (CCK).Fatty acids and amino acids (products of digestion) in the duodenum stimulate the release of CCK, which causes gallbladder contraction and opens the sphincter of Oddi. CCK also stimulates vagal nerve endings, bringing about the release of acetylcholine (ACh), which also stimulates the gallbladder. Reference: Sircar Principles of Medical Physiology, 1st ed, Page: 444