This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
[{'content': 'Which vitamin is synthesized by intestinal sites? \nSelect and explain. \nA. Vit B, B. Vit A, C. Vit D, D. Vit K', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Three compounds have the biological activity of vitamin K phylloquinone, the normal dietary source, found in green vegetables; menaquinones, synthesized by intestinal bacteria, menadione and menadiol diacetate, synthetic compounds that can be metabolized to phylloquinone menaquinone is synthesized in the intestinal site by the intestinal bacteria Ref: Harper 30e, page: 554', 'role': 'assistant'}]