Why did the instructor describe nutrition as a "relatively new" and "inherently complex" science?

• A. Because it only studies modern processed foods and ignores traditional diets and historical patterns of disease.
• B. Because all nutrients have been fully identified for centuries and the remaining questions are mainly about culinary taste preferences, which makes research trivial.
• C. Because nutrition research primarily focuses on a fixed set of biochemical pathways and has long-standing universal recommendations that never change, therefore complexity is overstated.
• D. Because food composition, human biology, and human behavior interact in many ways and our scientific understanding is still evolving.

Answer: (D)