Please explain

Manufacturer's conclusion: the pesticide used is not hazardous to humans if absorbed into edible pants. Why? Because ounce for ounce the active ingredient in this pesticide is less toxic than the active ingredient in mouthwash. What's the issue here? We are comparing the hazards of ingesting toxins from mouth wash and ingesting toxins from edible plants. Well, humans probably ingest more EDIBLE plants than they ingest mouth wash. Thus, we cannot accurately compare the two because the amount of mouthwash a human ingests is much smaller than the amount of edible plant a human ingests. Answer choice (B) points this out exactly. Hope that clears things up! Please let us know if you have any other questions.

Thank you.

I understand why B, but C was tempting!! Why not C?

(C) is irrelevant here. The issue here is whether or not this pesticide is harmful if absorbed into edible plants.