The thiazide diuretics (e.g., hydrochlorothiazide, chlorothiazide, benzthiazide) promote diuresis by inhibiting reabsorption of NaCl, primarily in the early distal tubule. Ethacrynic acid and furosemide are both loop diuretics. They act by inhibiting electrolyte reabsorption in the thick ascending loop of Henle. Note that even if you didn't know where these agents act, if you knew that they both belonged to the same class of diuretics, you could have eliminated them both as possibilities since there can't be more than one correct answer choice. Mannitol is an osmotic diuretic. It is freely filtered at the glomerulus and is not reabsorbed. Its primary action occurs at the proximal tubule. Ref: Michel T., Hoffman B.B. (2011). Chapter 27. Treatment of Myocardial Ischemia and Hypeension. In B.C. Knollmann (Ed), Goodman & Gilman's The Pharmacological Basis of Therapeutics, 12e.