This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal System, Subject name: Physiology
Which of the following is the strongest cholagogue? 
Select and explain. 
A. Vagus nerve/Ach, B. Cholecystokinin, C. Bile acids, D. Secretin
B: Cholecystokinin
Answer: B: Cholecystokinin 
Explanation: Cholagogues are the substances that increase the bile flow by causing gall bladder contraction. CCK is a cholagogue. Vagus nerve, bile acids are choleretics; they increase the bile secretion from liver.