A district administration pays villagers thirty rupees for every sack of uprooted water hyacinth brought to the tank bund, so that the district's tanks may be cleared of the weed. It reports that the sacks brought in have risen from 2,000 in the first year to 26,000 in the third, and holds that the tanks are being cleared at a growing rate. Which of the following, if true, most weakens the administration's position?

The administration pays for sacks delivered but wants tanks cleared, and the two hold together only while the sole way to get a sack is to take it out of a tank. Once it pays to grow the weed, sacks can multiply while the tanks fill up, and the very shallows being cultivated are the water the payment was meant to clear — so the thirteenfold rise may measure the strength of the incentive rather than any clearing at all. An unchanged rate of thirty rupees says nothing about where the weed comes from; composting the weed is a use for it after collection; and the number and ownership of the tanks describe the district without touching the source of the sacks.