The same number of eggplant seedlings were planted in the two experimental greenhouses, and only fertilizer A was applied to the first greenhouse, but not to the second greenhouse. The first greenhouse produces 1200 kilograms of eggplant and the second greenhouse produces 900kg eggplant. Nothing but water was applied to the two greenhouses, so fertilizer A must have led to a higher yield of eggplant in the first greenhouse.
The statement 'The quality of the soil and the amount of sunshine in the two greenhouses are different' most seriously weakens the above argument.