Among the four alternatives, Ten alone satisfies the full historical condition. Dahsala used a ten-year average of crop yields and prices to frame cash revenue rates, reducing dependence on a single season's fluctuation. The distractors need separate rejection: Twenty belongs to a different institution, context or chronology; Five does not perform the function described in the stem; and Twelve fails the required association. The wording of “Todar Mal's dahsala calculation was based on averages covering how many years?” is deliberately specific, so the candidate should isolate its operative clue before recalling names. — Ten”, but also remember the factual reason stated above.