Final answer:
Agricultural foods shifted nutrition from a varied diet to one focused on carbohydrates and poorer-quality protein due to the transition to sedentary farming which led to dependence on fewer crop varieties.
Step-by-step explanation:
The shift from nomadic hunter-gatherers to sedentary agricultural societies led to a significant change in diet. The development of agriculture, especially the cultivation of crops like rice, wheat, and potatoes, ushered in a diet that focused heavily on carbohydrates. Additionally, this transition resulted in people consuming less diverse and lower-nutrient foods, with a tendency towards poorer-quality protein as opposed to the varied and nutrient-rich diet of a hunter-gatherer, which included a wide array of plant-based foods and lean meats.
Thus, the correct answer to the student's question is: Agricultural foods eventually shifted nutrition from a generalized diet to one focused on (a) carbohydrates and (d) poorer-quality protein.