Ans. is 'c' ie carbonic anhydrase (Ref: Parson, 19/e, p166; Kanski, 5/e, p193; Chatterjee Shinde Biochemistry. 6/e, p629).Nowhere could 1 find a direct answer. The points in favour of the above answer are --Of all the above options, carbonic anhydrase is the only enzyme which catalyzes the reversible reaction :CO2+H2O =H2 CO3Kanski writes - "Aqueous humor is actively secreted by the non pigmented epithelium as a result of a metabolic process that depends on several enzyme systems, specially the Na+/K+ ATPase pump, which secretes Na+ ions into the posterior chamber. Water follows passively along the osmotic gradient. Carbonic anhydrase also plays a role, but the precise mechanism is uncertain."Parson writes - "Carbonic anhydrase inhibitors block the action of carbonic anhydrase and reduce the production of aqueous in the eye."