Inorganic pesticides remain active on the surfaces of fruits and vegetables for several days after spraying, while organic pesticides dissipate within a few hours after application, leaving the surface of the sprayed produce free of pesticide residue. Therefore, when purchasing from a farm that uses inorganic pesticides, one must be careful to wash the produce thoroughly before eating it to prevent the ingestion of toxins. But one need not worry about ingesting pesticides when purchasing from farms that use only organic pesticides.
The argument above assumes that
The conclusion of the argument is that one need not worry about ingesting pesticides when purchasing produce from farms that use only organic pesticides. The basis for that claim is the fact that organic pesticides leave the surface of produce within a few hours of spraying. In order for this argument to be valid, we must assume that the organic pesticides do not harm the produce in any lasting way.
(A) This is unrelated to the argument since the conclusion speaks about not having to worry about ingesting produce on which only organic pesticides were known to be used.
(B) If anything, this statement runs counter to what the argument is saying. If produce that has been sprayed with organic pesticide reaches the final consumer within hours after it is picked, it is possible that the consumer does need be concerned about the pesticides.
(C) The conclusion of the argument is already limited to those farms which use "only organic pesticides."
(D) CORRECT.If a pesticide is capable of penetrating the skin of a fruit or vegetable then, while the organic pesticide will dissipate from the surface of the fruit in a few hours, it may remain inside the fruit. The author of this argument assumes that the pesticides cannot penetrate the skin.