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: Radiology
Which is not required for visualisation of gallbladder in oral cholecystography – 
Select and explain. 
A. Functioning liver, B. Motor mechanisms of gall bladder, C. Patency of cystic duct, D. Ability to absorb water
B: Motor mechanisms of gall bladder
Answer: B: Motor mechanisms of gall bladder 
Explanation: Visualization of the gallbladder in OCG depends on:-

Ingestion of dye
Absorption of dye in gut
Blood flow to liver (Entero-hepatic-circulation)
Take up in liver (functional liver), ability of liver to excrete dye into the bile (functional liver)
The ability of gallbladder to concentrate the excreted dye (by absorbing water)
Patency of hepatic & cystic duct system