Gardener: Researchers encourage us to allow certain kinds of weeds to grow among garden vegetables because they can repel caterpillars from the garden. While it is wise to avoid unnecessary use of insecticides, the researchers' advice is premature. For all we know, those kinds of weeds can deplete the soil of nutrients and moisture that garden crops depend on, and might even attract other kinds of damaging pests. Which one of the following most accurately expresses the main conclusion of the gardener's argument? ['Allowing certain kinds of weeds to grow in vegetable gardens may contribute to a net increase in unwanted garden pests.', 'Allowing the right kinds of weeds to grow in vegetable gardens can help toward controlling caterpillars without the use of insecticides.', 'To the extent that it is possible to do so, we should eliminate the use of insecticides in gardening.', 'We should be cautious about the practice of allowing certain kinds of weeds to grow among garden vegetables.']