Final answer:
Vitamin B12 is the only nutrient among the options given that cannot be naturally obtained from a plant-based diet because it is produced by bacteria and primarily found in animal products.The correct option is C.
Step-by-step explanation:
Not all vitamins and minerals can be readily obtained from a diet consisting of vegetables, fruits, beans, nuts, and whole grains alone. Among the options given, Vitamin B12 is the one that cannot be obtained from these plant-based sources. Vitamin B12 is produced by bacteria and is mainly found in animal products. Although some plant-based foods are fortified with B12, it's naturally absent from fruits and vegetables. Therefore, vegetarians and vegans need to be conscious of their vitamin B12 intake and consider supplements or fortified foods. Vitamin D can be synthesized by the body in the presence of sunlight, while Iron and Vitamin C are readily available in plant-based foods.