A silk-reeling cluster is being urged to build a shared tank in which waste water can be settled and used again, on the ground that a cluster in another district cut its water charges by a third after building one. Which of the following, if true, most supports the expectation that the same saving can be had here?

Borrowing a result requires that the thing which produced it be present here too. Identical basins drawing identical quantities make the saving a matter of the reeling itself, and ruling out a tariff change removes the one route by which the other cluster's gain might have had nothing to do with its tank. A grant now withdrawn bears on the cost of building, the cluster's greater age proves nothing about water use, and a shared contractor builds the tank without making the two clusters alike.