In an attempt to counter complaints that a certain pesticide is potentially hazardous to humans if absorbed into edible plants, the pesticide manufacturer has advertised that "ounce for ounce, the active ingredient in this pesticide is less toxic than the active ingredient in mouthwash. " Which one of the following, if true, indicates a weakness in the manufacturer's argument? ['On average, the toxins present in the pesticide take longer than the toxins present in mouthwash to reach harmful levels in the human body.', 'Since the government began to regulate the pesticide industry over ten years ago, there has been a growing awareness of the dangers of toxins used in pesticides.', 'The quantity of toxins humans ingest by consuming plants treated with the pesticide is, on average, much higher than the quantity of toxins humans ingest by using mouthwash.', 'The ounce-for-ounce toxicity of the active ingredient in mouthwash is less than that of most products meant for external use by humans, such as nail polish or other cosmetics.']