This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Physiology
Free water clearance by the kidney is increased by which of the following? 
Select and explain. 
A. Diabetes insipidus, B. Renal failure, C. Diuretic therapy, D. Diabetes mellitus
A: Diabetes insipidus
Answer: A: Diabetes insipidus 
Explanation: Free water clearance is the amount of water excreted in excess of that required to make the urine isotonic to plasma.