Answer:
D
Explanation:
Based on the context and key points, such as "... as the earliest humans had to recognize which plants were safe to eat," answer D is the best choice. We know toxicology would have had to change significantly because it is a science and science always evolves, so A is out. Toxicology is NOT the study of just "safe" plants, so B is out. Lastly, those who study toxicology do not all study foods, so C is out.