Free water clearance is decreased by

Flurosemide is a drug which act on both coex and medulla. It acts on the ascending limb of loop of Henle which has both coical and medullary components.Thus,furosemide can block positive as well as negative free water clearance. Vincristine increases the secretion of the harmone ADH and thus decreases positive free water clearance. Chlorpropamide sensitizes the kidney to ADH action.Thus it may decrease the positive free water clearance and in some patients may results in hyponatremia and water intoxication. Most probably the question should have been framed as "All of the following blocks free water clearance,except" But if you have to choose one answer,go for furosemide as it will always block free water clearance where as other drugs will cause them occasionally as it is their adverse effect.