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: Pharmacology
Vasopressin decreases the volume of urine primarily by causing : 
Select and explain. 
A. Decrease in glomerular filtration rate, B. Decrease in renal blood flow, C. Decrease in water permeability of descending limb of loop of Henle, D. Increase in water permeability of collecting duct cells
D: Increase in water permeability of collecting duct cells
Answer: D: Increase in water permeability of collecting duct cells 
Explanation: None